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C++ || Custom Template Hash Map With Iterator Using Separate Chaining

June 11, 2013 admin No comments

Before we get into the code, what is a Hash Map? Simply put, a Hash Map is an extension of a Hash Table; which is a data structure used to map unique “keys” to specific “values.” The Hash Map demonstrated on this page is different from the previous Hash Table implementation in that key/value pairs do not need to be the same datatype, they can be completely different. So for example, if you wish to map a string “key” to an integer “value“, utilizing a Hash Map is ideal.

In its most simplest form, a Hash Map can be thought of as an associative array, or a “dictionary.” Hash Map’s are composed of a collection of key/value pairs, such that each possible key appears atleast once in the collection for a given value. While a standard array requires that indice subscripts be integers, a hash map can use a string, an integer, or even a floating point value as the index. That index is called the “key,” and the contents within the array at that specific index location is called the “value.” A hash map uses a hash function to generate an index into the table, creating buckets or slots, from which the correct value can be found.

To illustrate, suppose that you’re working with some data that has values associated with strings — for instance, you might have student names and you wish to assign them grades. How would you store this data? Depending on your skill level, you might use multiple arrays during the implementation. For example, in terms of a one dimensional array, if we wanted to access the data for a student located at index #25, we could access it by doing:

studentNames[25]; // do something with the data studentGrades[25];

Here, we dont have to search through each element in the array to find what we need, we just access it at index #25. The question is, how do we know that index #25 holds the data that we are looking for? If we have a large set of data, not only will keeping track of multiple arrays become tiresome, but doing a sequential search over each item within the separate arrays can become very inefficient. That is where hashing comes in handy. Using a Hash Map, we can use the students name as the “key,” and the students grade as the data “value.” Given this “key” (the students name), we can apply a hash function to map a unique index or bucket within the hash table to find the data “value” (the students grade) that we wish to access.

So in essence, a Hash Map is an extension of a hash table, which is a data structure that stores key/value pairs. Hash tables are typically used because they are ideal for doing a quick search of items.

Though hashing is ideal, it isnt perfect. It is possible for multiple “keys” to be hashed into the same location. Hash “collisions” are practically unavoidable when hashing large data sets. The code demonstrated on this page handles collisions via separate chaining, utilizing an array of linked list head nodes to store multiple keys within one bucket – should any collisions occur.

A special feature of this current hash map class is that its implemented as a multimap, meaning that more than one “value” can be associated with a given “key.” For example, in a student enrollment system where students may be enrolled in multiple classes simultaneously, there might be an association for each enrollment where the “key” is the student ID, and the “value” is the course ID. In this example, if a given student is enrolled in three courses, there will be three associated “values” (course ID’s) for one “key” (student ID) in the Hash Map.

An iterator was also implemented, making data access that much more simple within the hash map class. Click here for an overview demonstrating how custom iterators can be built.

=== CUSTOM TEMPLATE HASH MAP WITH ITERATOR ===





		
		
			#include 'HashMap.h' - Hash Map With Iterator
			
C++
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   June 11, 2013
//    Taken From: http://programmingnotes.org/
//    File:  HashMap.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a Hash Map.
// ============================================================================
#ifndef TEMPLATE_HASH_MAP
#define TEMPLATE_HASH_MAP
#include <iostream>
#include <string>
#include <sstream>
#include <cstdlib>

// if user doesnt define, this is the
// default hash map size
const int HASH_SIZE = 350;

template <class Key, class Value>
class HashMap
{
public:
    HashMap(int hashSze = HASH_SIZE);
        /*   Function: Constructor initializes hash map
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty(int keyIndex);
        /*   Function: Determines whether hash map is empty at the given hash
                            map key index
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is empty and the
                             function = false if hash map is not empty */
    bool  IsFull();
        /*   Function: Determines whether hash map is full
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is full and the
                             function = false if hash map is not full */
    int Hash(Key m_key);
        /*   Function: Computes and returns a hash map key index for a given item
                        The returned key index is the given cell where the item resides
            Precondition:  Hash map has been created and is not full
            Postcondition: The hash key is returned */
    void Insert(Key m_key, Value m_value);
        /*   Function: Adds new item to the back of the list at a given key in the hash map
                         A unique hash key is automatically generated for each new item
            Precondition:  Hash map has been created and is not full
            Postcondition: Item is in the hash map */
    bool Remove(Key m_key, Value deleteItem);
        /*   Function: Removes the first instance from the map whose value is "deleteItem"
            Precondition:  Hash map has been created and is not empty
            Postcondition: The function = true if deleteItem is found and the
                             function = false if deleteItem is not found */
    void Sort(int keyIndex);
        /*   Function: Sort the items in the map at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The hash map is sorted */
    int TableSize();
        /*   Function: Return the size of the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int TotalElems();
        /*   Function: Return the total number of elements contained in the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int BucketSize(int keyIndex);
        /*   Function: Return the number of items contained in the hash map
                        cell at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The size of the given key cell is returned */
    int Count(Key m_key, Value searchItem);
        /*   Function: Return the number of times searchItem appears in the map
                        at the given key
            Precondition: Hash map has been initialized
            Postcondition: The number of times searchItem appears in the map is returned */
    int ContainsKey(Key m_key);
        /*   Function: Return the number of times the given key appears in the hashmap
            Precondition: Hash map has been initialized
            Postcondition: The number of times the given key appears in the map is returned */
    void MakeEmpty();
        /*   Function: Initializes hash map to an empty state
            Precondition: Hash map has been created
            Postcondition: Hash map no longer exists */
    ~HashMap();
        /*   Function: Removes the hash map
            Precondition: Hash map has been declared
            Postcondition: Hash map no longer exists */

    //  -- ITERATOR CLASS --
    class Iterator;
        /*   Function: Class declaration to the iterator
            Precondition: Hash map has been declared
            Postcondition: Hash Iterator has been declared */

    Iterator begin(int keyIndex){return(!IsEmpty(keyIndex)) ? head[keyIndex]:NULL;}
        /*   Function: Returns the beginning of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */

    Iterator end(int keyIndex=0){return NULL;}
        /*   Function: Returns the end of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */

private:
    struct KeyValue  // struct to hold key/value pairs
    {
        Key key;
        Value value;
    };
    struct node
    {
        KeyValue currentItem;
        node* next;
    };
    node** head; // array of linked list declaration - front of each hash map cell
    int hashSize; // the size of the hash map (how many cells it has)
    int totElems; // holds the total number of elements in the entire table
    int* bucketSize; // holds the total number of elems in each specific hash map cell
};

//=========================  Implementation  ================================//

template <class Key, class Value>
HashMap<Key, Value>::HashMap(int hashSze)
{
    hashSize = hashSze;
    head = new node*[hashSize];
    bucketSize = new int[hashSize];
    for(int x=0; x < hashSize; ++x)
    {
        head[x] = NULL;
        bucketSize[x] = 0;
    }
    totElems = 0;
}/* End of HashMap */

template <class Key, class Value>
bool HashMap<Key, Value>::IsEmpty(int keyIndex)
{
    if(keyIndex >=0 && keyIndex < hashSize)
    {
        return head[keyIndex] == NULL;
    }
    return true;
}/* End of IsEmpty */

template <class Key, class Value>
bool HashMap<Key, Value>::IsFull()
{
    try
    {
        node* location = new node;
        delete location;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}/* End of IsFull */

template <class Key, class Value>
int HashMap<Key, Value>::Hash(Key m_key)
{
    long h = 19937;
    std::stringstream convert;

    // convert the parameter to a string using "stringstream" which is done
    // so we can hash multiple datatypes using only one function
    convert << m_key;
    std::string temp = convert.str();

    for(unsigned x=0; x < temp.length(); ++x)
    {
        h = (h << 6) ^ (h >> 26) ^ temp[x];
    }
    return abs(h % hashSize);
} /* End of Hash */

template <class Key, class Value>
void HashMap<Key, Value>::Insert(Key m_key, Value m_value)
{
    if(IsFull())
    {
        //std::cout<<"\nINSERT ERROR - HASH MAP FULL\n";
    }
    else
    {
        int keyIndex = Hash(m_key);
        node* newNode = new node;   // add new node
        newNode-> currentItem.key = m_key;
        newNode-> currentItem.value = m_value;
        newNode-> next = NULL;

        if(IsEmpty(keyIndex))
        {
            head[keyIndex] = newNode;
        }
        else
        {
            node* temp = head[keyIndex];
            while(temp-> next != NULL)
            {
                temp = temp-> next;
            }
            temp-> next = newNode;
        }
        ++bucketSize[keyIndex];
        ++totElems;
    }
}/* End of Insert */

template <class Key, class Value>
bool HashMap<Key, Value>::Remove(Key m_key, Value deleteItem)
{
    bool isFound = false;
    node* temp;
    int keyIndex = Hash(m_key);

    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nREMOVE ERROR - HASH MAP EMPTY\n";
    }
    else if(head[keyIndex]->currentItem.key == m_key
            && head[keyIndex]->currentItem.value == deleteItem)
    {
        temp = head[keyIndex];
        head[keyIndex] = head[keyIndex]-> next;
        delete temp;
        --totElems;
        --bucketSize[keyIndex];
        isFound = true;
    }
    else
    {
        for(temp = head[keyIndex];temp->next!=NULL;temp=temp->next)
        {
            if(temp->next->currentItem.key == m_key
                && temp->next->currentItem.value == deleteItem)
            {
                node* deleteNode = temp->next;
                temp-> next = temp-> next-> next;
                delete deleteNode;
                isFound = true;
                --totElems;
                --bucketSize[keyIndex];
                break;
            }
        }
    }
    return isFound;
}/* End of Remove */

template <class Key, class Value>
void HashMap<Key, Value>::Sort(int keyIndex)
{
    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nSORT ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        int listSize = BucketSize(keyIndex);
        bool sorted = false;

        do{
            sorted = true;
            int x = 0;
            for(node* temp = head[keyIndex];
                temp->next!=NULL && x < listSize-1;
                temp=temp->next,++x)
            {
                if(temp-> currentItem.value > temp->next->currentItem.value)
                {
                    std::swap(temp-> currentItem,temp->next->currentItem);
                    sorted = false;
                }
            }
            --listSize;
        }while(!sorted);
    }
}/* End of Sort */

template <class Key, class Value>
int HashMap<Key, Value>::TableSize()
{
    return hashSize;
}/* End of TableSize */

template <class Key, class Value>
int HashMap<Key, Value>::TotalElems()
{
    return totElems;
}/* End of TotalElems */

template <class Key, class Value>
int HashMap<Key, Value>::BucketSize(int keyIndex)
{
    return(!IsEmpty(keyIndex)) ? bucketSize[keyIndex]:0;
}/* End of BucketSize */

template <class Key, class Value>
int HashMap<Key, Value>::Count(Key m_key, Value searchItem)
{
    int keyIndex = Hash(m_key);
    int search = 0;

    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nCOUNT ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)
        {
            if(temp->currentItem.key == m_key
                && temp->currentItem.value == searchItem)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of Count */

template <class Key, class Value>
int HashMap<Key, Value>::ContainsKey(Key m_key)
{
    int keyIndex = Hash(m_key);
    int search = 0;

    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nCONTAINS KEY ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)
        {
            if(temp->currentItem.key == m_key)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of ContainsKey */

template <class Key, class Value>
void HashMap<Key, Value>::MakeEmpty()
{
    totElems = 0;
    for(int x=0; x < hashSize; ++x)
    {
        if(!IsEmpty(x))
        {
            //std::cout << "Destroying nodes ...\n";
            while(!IsEmpty(x))
            {
                node* temp = head[x];
                //std::cout << temp-> currentItem.value <<std::endl;
                head[x] = head[x]-> next;
                delete temp;
            }
        }
        bucketSize[x] = 0;
    }
}/* End of MakeEmpty */

template <class Key, class Value>
HashMap<Key, Value>::~HashMap()
{
    MakeEmpty();
    delete[] head;
    delete[] bucketSize;
}/* End of ~HashMap */

//   END OF THE HASH MAP CLASS
// -----------------------------------------------------------
//   START OF THE HASH MAP ITERATOR CLASS

template <class Key, class Value>
class HashMap<Key, Value>::Iterator :
        public std::iterator<std::forward_iterator_tag,Value>,
        public HashMap<Key, Value>
    {
public:
    // Iterator constructor
    Iterator(node* otherIter = NULL)
    {
        itHead = otherIter;
    }
    ~Iterator() {}
    // The assignment and relational operators are straightforward
    Iterator& operator=(const Iterator& other)
    {
        itHead = other.itHead;
        return(*this);
    }
    bool operator==(const Iterator& other)const
    {
        return itHead == other.itHead;
    }
    bool operator!=(const Iterator& other)const
    {
        return itHead != other.itHead;
    }
    bool operator<(const Iterator& other)const
    {
        return itHead < other.itHead;
    }
    bool operator>(const Iterator& other)const
    {
        return other.itHead < itHead;
    }
    bool operator<=(const Iterator& other)const
    {
        return (!(other.itHead < itHead));
    }
    bool operator>=(const Iterator& other)const
    {
        return (!(itHead < other.itHead));
    }
    // Update my state such that I refer to the next element in the
    // HashMap.
    Iterator operator+(int incr)
    {
        node* temp = itHead;
        for(int x=0; x < incr && temp!= NULL; ++x)
        {
            temp = temp->next;
        }
        return temp;
    }
    Iterator operator+=(int incr)
    {
        for(int x=0; x < incr && itHead!= NULL; ++x)
        {
            itHead = itHead->next;
        }
        return itHead;
    }
    Iterator& operator++() // pre increment
    {
        if(itHead != NULL)
        {
            itHead = itHead->next;
        }
        return(*this);
    }
    Iterator operator++(int) // post increment
    {
        node* temp = itHead;
        this->operator++();
        return temp;
    }
    KeyValue& operator[](int incr)
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL || (*this + incr) == NULL)
        {
            return junk;
        }
        return(*(*this + incr));
    }
    // Return a reference to the value in the node.  I do this instead
    // of returning by value so a caller can update the value in the
    // node directly.
    KeyValue& operator*()
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL)
        {
            return junk;
        }
        return itHead->currentItem;
    }
    KeyValue* operator->()
    {
        return(&**this);
    }
private:
    node* itHead;
    KeyValue junk;
};
#endif // http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   June 11, 2013
//    Taken From: http://programmingnotes.org/
//    File:  HashMap.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a Hash Map.
// ============================================================================
#ifndef TEMPLATE_HASH_MAP
#define TEMPLATE_HASH_MAP
#include <iostream>
#include <string>
#include <sstream>
#include <cstdlib>
 
// if user doesnt define, this is the
// default hash map size
const int HASH_SIZE = 350;
 
template <class Key, class Value>
class HashMap
{
public:
    HashMap(int hashSze = HASH_SIZE);
        /*   Function: Constructor initializes hash map
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty(int keyIndex);
        /*   Function: Determines whether hash map is empty at the given hash
                            map key index
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is empty and the
                             function = false if hash map is not empty */
    bool  IsFull();
        /*   Function: Determines whether hash map is full
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is full and the
                             function = false if hash map is not full */
    int Hash(Key m_key);
        /*   Function: Computes and returns a hash map key index for a given item
                        The returned key index is the given cell where the item resides
            Precondition:  Hash map has been created and is not full
            Postcondition: The hash key is returned */
    void Insert(Key m_key, Value m_value);
        /*   Function: Adds new item to the back of the list at a given key in the hash map
                         A unique hash key is automatically generated for each new item
            Precondition:  Hash map has been created and is not full
            Postcondition: Item is in the hash map */
    bool Remove(Key m_key, Value deleteItem);
        /*   Function: Removes the first instance from the map whose value is "deleteItem"
            Precondition:  Hash map has been created and is not empty
            Postcondition: The function = true if deleteItem is found and the
                             function = false if deleteItem is not found */
    void Sort(int keyIndex);
        /*   Function: Sort the items in the map at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The hash map is sorted */
    int TableSize();
        /*   Function: Return the size of the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int TotalElems();
        /*   Function: Return the total number of elements contained in the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int BucketSize(int keyIndex);
        /*   Function: Return the number of items contained in the hash map
                        cell at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The size of the given key cell is returned */
    int Count(Key m_key, Value searchItem);
        /*   Function: Return the number of times searchItem appears in the map
                        at the given key
            Precondition: Hash map has been initialized
            Postcondition: The number of times searchItem appears in the map is returned */
    int ContainsKey(Key m_key);
        /*   Function: Return the number of times the given key appears in the hashmap
            Precondition: Hash map has been initialized
            Postcondition: The number of times the given key appears in the map is returned */
    void MakeEmpty();
        /*   Function: Initializes hash map to an empty state
            Precondition: Hash map has been created
            Postcondition: Hash map no longer exists */
    ~HashMap();
        /*   Function: Removes the hash map
            Precondition: Hash map has been declared
            Postcondition: Hash map no longer exists */
 
    //  -- ITERATOR CLASS --
    class Iterator;
        /*   Function: Class declaration to the iterator
            Precondition: Hash map has been declared
            Postcondition: Hash Iterator has been declared */
 
    Iterator begin(int keyIndex){return(!IsEmpty(keyIndex)) ? head[keyIndex]:NULL;}
        /*   Function: Returns the beginning of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */
 
    Iterator end(int keyIndex=0){return NULL;}
        /*   Function: Returns the end of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */
 
private:
    struct KeyValue  // struct to hold key/value pairs
    {
        Key key;
        Value value;
    };
    struct node
    {
        KeyValue currentItem;
        node* next;
    };
    node** head; // array of linked list declaration - front of each hash map cell
    int hashSize; // the size of the hash map (how many cells it has)
    int totElems; // holds the total number of elements in the entire table
    int* bucketSize; // holds the total number of elems in each specific hash map cell
};
 
//=========================  Implementation  ================================//
 
template <class Key, class Value>
HashMap<Key, Value>::HashMap(int hashSze)
{
    hashSize = hashSze;
    head = new node*[hashSize];
    bucketSize = new int[hashSize];
    for(int x=0; x < hashSize; ++x)
    {
        head[x] = NULL;
        bucketSize[x] = 0;
    }
    totElems = 0;
}/* End of HashMap */
 
template <class Key, class Value>
bool HashMap<Key, Value>::IsEmpty(int keyIndex)
{
    if(keyIndex >=0 && keyIndex < hashSize)
    {
        return head[keyIndex] == NULL;
    }
    return true;
}/* End of IsEmpty */
 
template <class Key, class Value>
bool HashMap<Key, Value>::IsFull()
{
    try
    {
        node* location = new node;
        delete location;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}/* End of IsFull */
 
template <class Key, class Value>
int HashMap<Key, Value>::Hash(Key m_key)
{
    long h = 19937;
    std::stringstream convert;
 
    // convert the parameter to a string using "stringstream" which is done
    // so we can hash multiple datatypes using only one function
    convert << m_key;
    std::string temp = convert.str();
 
    for(unsigned x=0; x < temp.length(); ++x)
    {
        h = (h << 6) ^ (h >> 26) ^ temp[x];
    }
    return abs(h % hashSize);
} /* End of Hash */
 
template <class Key, class Value>
void HashMap<Key, Value>::Insert(Key m_key, Value m_value)
{
    if(IsFull())
    {
        //std::cout<<"\nINSERT ERROR - HASH MAP FULL\n";
    }
    else
    {
        int keyIndex = Hash(m_key);
        node* newNode = new node;   // add new node
        newNode-> currentItem.key = m_key;
        newNode-> currentItem.value = m_value;
        newNode-> next = NULL;
 
        if(IsEmpty(keyIndex))
        {
            head[keyIndex] = newNode;
        }
        else
        {
            node* temp = head[keyIndex];
            while(temp-> next != NULL)
            {
                temp = temp-> next;
            }
            temp-> next = newNode;
        }
        ++bucketSize[keyIndex];
        ++totElems;
    }
}/* End of Insert */
 
template <class Key, class Value>
bool HashMap<Key, Value>::Remove(Key m_key, Value deleteItem)
{
    bool isFound = false;
    node* temp;
    int keyIndex = Hash(m_key);
 
    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nREMOVE ERROR - HASH MAP EMPTY\n";
    }
    else if(head[keyIndex]->currentItem.key == m_key
            && head[keyIndex]->currentItem.value == deleteItem)
    {
        temp = head[keyIndex];
        head[keyIndex] = head[keyIndex]-> next;
        delete temp;
        --totElems;
        --bucketSize[keyIndex];
        isFound = true;
    }
    else
    {
        for(temp = head[keyIndex];temp->next!=NULL;temp=temp->next)
        {
            if(temp->next->currentItem.key == m_key
                && temp->next->currentItem.value == deleteItem)
            {
                node* deleteNode = temp->next;
                temp-> next = temp-> next-> next;
                delete deleteNode;
                isFound = true;
                --totElems;
                --bucketSize[keyIndex];
                break;
            }
        }
    }
    return isFound;
}/* End of Remove */
 
template <class Key, class Value>
void HashMap<Key, Value>::Sort(int keyIndex)
{
    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nSORT ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        int listSize = BucketSize(keyIndex);
        bool sorted = false;
 
        do{
            sorted = true;
            int x = 0;
            for(node* temp = head[keyIndex];
                temp->next!=NULL && x < listSize-1;
                temp=temp->next,++x)
            {
                if(temp-> currentItem.value > temp->next->currentItem.value)
                {
                    std::swap(temp-> currentItem,temp->next->currentItem);
                    sorted = false;
                }
            }
            --listSize;
        }while(!sorted);
    }
}/* End of Sort */
 
template <class Key, class Value>
int HashMap<Key, Value>::TableSize()
{
    return hashSize;
}/* End of TableSize */
 
template <class Key, class Value>
int HashMap<Key, Value>::TotalElems()
{
    return totElems;
}/* End of TotalElems */
 
template <class Key, class Value>
int HashMap<Key, Value>::BucketSize(int keyIndex)
{
    return(!IsEmpty(keyIndex)) ? bucketSize[keyIndex]:0;
}/* End of BucketSize */
 
template <class Key, class Value>
int HashMap<Key, Value>::Count(Key m_key, Value searchItem)
{
    int keyIndex = Hash(m_key);
    int search = 0;
 
    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nCOUNT ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)
        {
            if(temp->currentItem.key == m_key
                && temp->currentItem.value == searchItem)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of Count */
 
template <class Key, class Value>
int HashMap<Key, Value>::ContainsKey(Key m_key)
{
    int keyIndex = Hash(m_key);
    int search = 0;
 
    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nCONTAINS KEY ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)
        {
            if(temp->currentItem.key == m_key)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of ContainsKey */
 
template <class Key, class Value>
void HashMap<Key, Value>::MakeEmpty()
{
    totElems = 0;
    for(int x=0; x < hashSize; ++x)
    {
        if(!IsEmpty(x))
        {
            //std::cout << "Destroying nodes ...\n";
            while(!IsEmpty(x))
            {
                node* temp = head[x];
                //std::cout << temp-> currentItem.value <<std::endl;
                head[x] = head[x]-> next;
                delete temp;
            }
        }
        bucketSize[x] = 0;
    }
}/* End of MakeEmpty */
 
template <class Key, class Value>
HashMap<Key, Value>::~HashMap()
{
    MakeEmpty();
    delete[] head;
    delete[] bucketSize;
}/* End of ~HashMap */
 
//   END OF THE HASH MAP CLASS
// -----------------------------------------------------------
//   START OF THE HASH MAP ITERATOR CLASS
 
template <class Key, class Value>
class HashMap<Key, Value>::Iterator :
        public std::iterator<std::forward_iterator_tag,Value>,
        public HashMap<Key, Value>
    {
public:
    // Iterator constructor
    Iterator(node* otherIter = NULL)
    {
        itHead = otherIter;
    }
    ~Iterator() {}
    // The assignment and relational operators are straightforward
    Iterator& operator=(const Iterator& other)
    {
        itHead = other.itHead;
        return(*this);
    }
    bool operator==(const Iterator& other)const
    {
        return itHead == other.itHead;
    }
    bool operator!=(const Iterator& other)const
    {
        return itHead != other.itHead;
    }
    bool operator<(const Iterator& other)const
    {
        return itHead < other.itHead;
    }
    bool operator>(const Iterator& other)const
    {
        return other.itHead < itHead;
    }
    bool operator<=(const Iterator& other)const
    {
        return (!(other.itHead < itHead));
    }
    bool operator>=(const Iterator& other)const
    {
        return (!(itHead < other.itHead));
    }
    // Update my state such that I refer to the next element in the
    // HashMap.
    Iterator operator+(int incr)
    {
        node* temp = itHead;
        for(int x=0; x < incr && temp!= NULL; ++x)
        {
            temp = temp->next;
        }
        return temp;
    }
    Iterator operator+=(int incr)
    {
        for(int x=0; x < incr && itHead!= NULL; ++x)
        {
            itHead = itHead->next;
        }
        return itHead;
    }
    Iterator& operator++() // pre increment
    {
        if(itHead != NULL)
        {
            itHead = itHead->next;
        }
        return(*this);
    }
    Iterator operator++(int) // post increment
    {
        node* temp = itHead;
        this->operator++();
        return temp;
    }
    KeyValue& operator[](int incr)
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL || (*this + incr) == NULL)
        {
            return junk;
        }
        return(*(*this + incr));
    }
    // Return a reference to the value in the node.  I do this instead
    // of returning by value so a caller can update the value in the
    // node directly.
    KeyValue& operator*()
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL)
        {
            return junk;
        }
        return itHead->currentItem;
    }
    KeyValue* operator->()
    {
        return(&**this);
    }
private:
    node* itHead;
    KeyValue junk;
};
#endif // http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The iterator class starts on line #381, and is built to support most of the standard relational operators, as well as arithmetic operators such as ‘+,+=,++’ (pre/post increment). The * (star), bracket [] and -> arrow operators are also supported. Click here for an overview demonstrating how custom iterators can be built.

The rest of the code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as many of its STL template class counterparts. Here are sample programs demonstrating its use.





		
		
			#1 - Demonstrate Basic Use
			
C++
			
			// DEMONSTRATE BASIC USE AND THE REMOVE / SORT FUNCTIONS
#include <iostream>
#include <string>
#include "HashMap.h"
using namespace std;

// iterator declaration
typedef HashMap<string, int>::Iterator iterDec;

int main()
{
    // declare variables
    HashMap<string, int> hashMap;
    
    // place items into the hash map using the 'insert' function
    // NOTE: its OK for dupicate keys to be inserted into the hash map
    hashMap.Insert("BIOL", 585);
    hashMap.Insert("CPSC", 386);
    hashMap.Insert("ART", 101);
    hashMap.Insert("CPSC", 462);
    hashMap.Insert("HIST", 251);
    hashMap.Insert("CPSC", 301);
    hashMap.Insert("MATH", 270);
    hashMap.Insert("PE", 145);
    hashMap.Insert("BIOL", 134);
    hashMap.Insert("GEOL", 201);
    hashMap.Insert("CIS", 465);
    hashMap.Insert("CPSC", 240);
    hashMap.Insert("GEOL", 101);
    hashMap.Insert("MATH", 150);
    hashMap.Insert("DANCE", 134);
    hashMap.Insert("CPSC", 131);
    hashMap.Insert("ART", 345);
    hashMap.Insert("CHEM", 185);
    hashMap.Insert("PE", 125);
    hashMap.Insert("CPSC", 120);
    
    // display the number of times the key "CPSC" appears in the hashmap
    cout<<"The key 'CPSC' appears in the hash map "<<
        hashMap.ContainsKey("CPSC")<<" time(s)\n";
    
    // declare an iterator for the "CPSC" key so we can display data to screen
    iterDec it = hashMap.begin(hashMap.Hash("CPSC"));
    
    // display the first value
    cout<<"\nThe first item with the key 'CPSC' is: "
        <<it[0].value<<endl;
    
    // display all the values in the hash map whose key matches "CPSC"
    // NOTE: its possible for multiple different keys types
    //   to be placed into the same hash map bucket    
    cout<<"\nThese are all the items in the hash map whose key is 'CPSC': \n";
    for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x)
    {
        if(it[x].key == "CPSC") // make sure this is the key we are looking for
        {
            cout<<"  Key-> "<<it[x].key<<"\tValue-> "<<it[x].value<<endl;
        }
    }
    
    // remove the first value from the key "CPSC"
    cout<<"\n[REMOVE THE VALUE '"<<it[0].value<<"' FROM THE KEY '"<<it[0].key<<"']\n";    
    hashMap.Remove("CPSC",it[0].value);
    
    // display the number of times the key "CPSC" appears in the hashmap
    cout<<"\nNow the key 'CPSC' only appears in the hash map "<<
        hashMap.ContainsKey("CPSC")<<" time(s)\n";     
    
    // update the iterator to the current hash map state
    it = hashMap.begin(hashMap.Hash("CPSC"));
    
    // sort the values in the hash map bucket whose key is "CSPC"
    hashMap.Sort(hashMap.Hash("CPSC"));
    
    // display the values whose key matches "CPSC"
    cout<<"\nThese are the sorted items in the hash map whose key is 'CPSC': \n";
    for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x)
    {
        if(it[x].key == "CPSC")
        {
            cout<<"  Key-> "<<it[x].key<<"\tValue-> "<<it[x].value<<endl;
        }
    }        
        
    // display all the key/values in the entire hash map 
    cout<<"\nThese are all of the items in the entire hash map: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            for(iterDec iter = hashMap.begin(x); iter != hashMap.end(x); ++iter)
            {
                cout<<"  Key-> "<<(*iter).key<<"\tValue-> "<<iter->value<<endl;
            }
            cout<<endl;
        }        
    }
    
    // display the total number of items in the hash map
    cout<<"The total number of items in the hash map is: "<<
        hashMap.TotalElems()<<endl;           
    
    return 0;
}// http://programmingnotes.org/
			
				
					
				
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						// DEMONSTRATE BASIC USE AND THE REMOVE / SORT FUNCTIONS
#include <iostream>
#include <string>
#include "HashMap.h"
using namespace std;
 
// iterator declaration
typedef HashMap<string, int>::Iterator iterDec;
 
int main()
{
    // declare variables
    HashMap<string, int> hashMap;
    
    // place items into the hash map using the 'insert' function
    // NOTE: its OK for dupicate keys to be inserted into the hash map
    hashMap.Insert("BIOL", 585);
    hashMap.Insert("CPSC", 386);
    hashMap.Insert("ART", 101);
    hashMap.Insert("CPSC", 462);
    hashMap.Insert("HIST", 251);
    hashMap.Insert("CPSC", 301);
    hashMap.Insert("MATH", 270);
    hashMap.Insert("PE", 145);
    hashMap.Insert("BIOL", 134);
    hashMap.Insert("GEOL", 201);
    hashMap.Insert("CIS", 465);
    hashMap.Insert("CPSC", 240);
    hashMap.Insert("GEOL", 101);
    hashMap.Insert("MATH", 150);
    hashMap.Insert("DANCE", 134);
    hashMap.Insert("CPSC", 131);
    hashMap.Insert("ART", 345);
    hashMap.Insert("CHEM", 185);
    hashMap.Insert("PE", 125);
    hashMap.Insert("CPSC", 120);
    
    // display the number of times the key "CPSC" appears in the hashmap
    cout<<"The key 'CPSC' appears in the hash map "<<
        hashMap.ContainsKey("CPSC")<<" time(s)\n";
    
    // declare an iterator for the "CPSC" key so we can display data to screen
    iterDec it = hashMap.begin(hashMap.Hash("CPSC"));
    
    // display the first value
    cout<<"\nThe first item with the key 'CPSC' is: "
        <<it[0].value<<endl;
    
    // display all the values in the hash map whose key matches "CPSC"
    // NOTE: its possible for multiple different keys types
    //   to be placed into the same hash map bucket    
    cout<<"\nThese are all the items in the hash map whose key is 'CPSC': \n";
    for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x)
    {
        if(it[x].key == "CPSC") // make sure this is the key we are looking for
        {
            cout<<"  Key-> "<<it[x].key<<"\tValue-> "<<it[x].value<<endl;
        }
    }
    
    // remove the first value from the key "CPSC"
    cout<<"\n[REMOVE THE VALUE '"<<it[0].value<<"' FROM THE KEY '"<<it[0].key<<"']\n";    
    hashMap.Remove("CPSC",it[0].value);
    
    // display the number of times the key "CPSC" appears in the hashmap
    cout<<"\nNow the key 'CPSC' only appears in the hash map "<<
        hashMap.ContainsKey("CPSC")<<" time(s)\n";     
    
    // update the iterator to the current hash map state
    it = hashMap.begin(hashMap.Hash("CPSC"));
    
    // sort the values in the hash map bucket whose key is "CSPC"
    hashMap.Sort(hashMap.Hash("CPSC"));
    
    // display the values whose key matches "CPSC"
    cout<<"\nThese are the sorted items in the hash map whose key is 'CPSC': \n";
    for(int x=0; x < hashMap.BucketSize(hashMap.Hash("CPSC")); ++x)
    {
        if(it[x].key == "CPSC")
        {
            cout<<"  Key-> "<<it[x].key<<"\tValue-> "<<it[x].value<<endl;
        }
    }        
        
    // display all the key/values in the entire hash map 
    cout<<"\nThese are all of the items in the entire hash map: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            for(iterDec iter = hashMap.begin(x); iter != hashMap.end(x); ++iter)
            {
                cout<<"  Key-> "<<(*iter).key<<"\tValue-> "<<iter->value<<endl;
            }
            cout<<endl;
        }        
    }
    
    // display the total number of items in the hash map
    cout<<"The total number of items in the hash map is: "<<
        hashMap.TotalElems()<<endl;           
    
    return 0;
}// http://programmingnotes.org/

SAMPLE OUTPUT:

The key 'CPSC' appears in the hash map 6 time(s)
The first item with the key 'CPSC' is: 386 These are all the items in the hash map whose key is 'CPSC': Key-> CPSC Value-> 386 Key-> CPSC Value-> 462 Key-> CPSC Value-> 301 Key-> CPSC Value-> 240 Key-> CPSC Value-> 131 Key-> CPSC Value-> 120 [REMOVE THE VALUE '386' FROM THE KEY 'CPSC'] Now the key 'CPSC' only appears in the hash map 5 time(s) These are the sorted items in the hash map whose key is 'CPSC': Key-> CPSC Value-> 120 Key-> CPSC Value-> 131 Key-> CPSC Value-> 240 Key-> CPSC Value-> 301 Key-> CPSC Value-> 462 These are all of the items in the entire hash map: Key-> CIS Value-> 465 Key-> DANCE Value-> 134 Key-> PE Value-> 145 Key-> PE Value-> 125 Key-> MATH Value-> 270 Key-> MATH Value-> 150 Key-> GEOL Value-> 201 Key-> GEOL Value-> 101 Key-> CPSC Value-> 120 Key-> CPSC Value-> 131 Key-> CPSC Value-> 240 Key-> CPSC Value-> 301 Key-> CPSC Value-> 462 Key-> BIOL Value-> 585 Key-> BIOL Value-> 134 Key-> ART Value-> 101 Key-> ART Value-> 345 Key-> CHEM Value-> 185 Key-> HIST Value-> 251
The total number of items in the hash map is: 19





		
		
			#2 - Display Items In A Struct
			
C++
			
			// DISPLAY ALL DATA INSIDE HASH MAP USING STD::STRING / INT / DOUBLE / STRUCT
#include <iostream>
#include <string>
#include "HashMap.h"
using namespace std;

// sample struct demo
struct MyStruct
{
    string car;
    int year;
    double mpg;
    
    // struct comparison operators
    // used for 'remove' function
    bool operator == (const MyStruct& rhs)const
    {
        return car == rhs.car &&
            year == rhs.year &&
            mpg == rhs.mpg;
    }    
    // used for 'sort' function
    bool operator > (const MyStruct& rhs)const
    {
        return car > rhs.car;
    }    
};// end of MyStruct

// iterator declaration
typedef HashMap<string, MyStruct>::Iterator iterDec;

int main()
{
    // declare variables
    MyStruct access; 
    HashMap<string, MyStruct> hashMap(10);
    
    // --- initialize data for car #1 ---
    access.car = "Ford Fusion";
    access.year = 2006;
    access.mpg = 28.5;        
    hashMap.Insert("Kenneth",access);            
    
    // --- initialize data for car #2 ---
    access.car = "BMW 535i";
    access.year = 2014;
    access.mpg = 25.4;
    hashMap.Insert("Kenneth",access);
    
    // --- initialize data for car #3 ---
    access.car = "Nissan Altima";
    access.year = 2011;
    access.mpg = 30.7;
    hashMap.Insert("Jessica",access);     
    
    // --- initialize data for car #4 ---
    access.car = "Acura Integra";
    access.year = 2001;
    access.mpg = 20.2;    
    hashMap.Insert("Kenneth",access);       
    
    
    // diplay how many cars "Kenneth" owns
    cout <<"'Kenneth' owns "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl;             
    
    // display all items in the hash map
    // NOTE: its possible for multiple different keys types
    //   to be placed into the same hash map bucket     
    cout<<"\nThese are all of the cars in the hash map: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            // initialize an iterator
            iterDec iter = hashMap.begin(x);
            
            // display the key
            cout<<(*iter).key<<"'s car(s)\n";
            // display all the values 
            for(;iter != hashMap.end(x); ++iter)
            {
                cout<<"\tCar: "<<iter->value.car
                    <<"\n\tYear: "<<iter->value.year
                    <<"\n\tMPG: "<<iter->value.mpg<<endl<<endl;                                
            }
        }        
    }               
    
    // display the number of items in the hash map
    cout<<"The total number of cars in the hash map is: "<<
        hashMap.TotalElems()<<endl;   
    
    // sort the cars that "Kenneth" owns by name
    cout<<"\nSorting the cars that 'Kenneth' owns by name.. \n";         
    hashMap.Sort(hashMap.Hash("Kenneth"));    
    
    // display all items in the hash map again  
    cout<<"\nAgain, these are all of the cars in the hash map: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            // initialize an iterator
            iterDec iter = hashMap.begin(x);
            
            // display the key
            cout<<iter->key<<"'s car(s)\n";
            // display all the values 
            for(;iter != hashMap.end(x); ++iter)
            {
                cout<<"\tCar: "<<(*iter).value.car
                    <<"\n\tYear: "<<(*iter).value.year
                    <<"\n\tMPG: "<<(*iter).value.mpg<<endl<<endl;                
            }
        }        
    } 

    // remove the car 'Acura Integra' from "Kenneth's" inventory
    for(iterDec iter = hashMap.begin(hashMap.Hash("Kenneth")); 
        iter != hashMap.end(hashMap.Hash("Kenneth")); ++iter)
    {		
        if(iter->value.car == "Acura Integra")
        {
            cout<<"'"<<iter->value.car<<"' has been removed from 'Kenneth's' inventory..\n";
            hashMap.Remove("Kenneth",(*iter).value);
            break;
        }
    }    
    
    // display how many cars "Kenneth" owns
    cout <<"\n'Kenneth' now owns only "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl;                 
    
    // display all items in the hash map one more time  
    cout<<"\nThese are all of the cars in the hash map with the 'Acura Integra' removed: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            // initialize an iterator
            iterDec iter = hashMap.begin(x);
            
            // display the key
            cout<<(*iter).key<<"'s car(s)\n";
            // display all the values 
            for(;iter != hashMap.end(x); ++iter)
            {
                cout<<"\tCar: "<<iter->value.car
                    <<"\n\tYear: "<<iter->value.year
                    <<"\n\tMPG: "<<iter->value.mpg<<endl<<endl;
            }
        }        
    }     
    
    // display the number of items in the hash map
    cout<<"The total number of cars in the hash map is: "<<
        hashMap.TotalElems()<<endl;               
    
    return 0;
}// http://programmingnotes.org/
			
				
					
				
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						// DISPLAY ALL DATA INSIDE HASH MAP USING STD::STRING / INT / DOUBLE / STRUCT
#include <iostream>
#include <string>
#include "HashMap.h"
using namespace std;
 
// sample struct demo
struct MyStruct
{
    string car;
    int year;
    double mpg;
    
    // struct comparison operators
    // used for 'remove' function
    bool operator == (const MyStruct& rhs)const
    {
        return car == rhs.car &&
            year == rhs.year &&
            mpg == rhs.mpg;
    }    
    // used for 'sort' function
    bool operator > (const MyStruct& rhs)const
    {
        return car > rhs.car;
    }    
};// end of MyStruct
 
// iterator declaration
typedef HashMap<string, MyStruct>::Iterator iterDec;
 
int main()
{
    // declare variables
    MyStruct access; 
    HashMap<string, MyStruct> hashMap(10);
    
    // --- initialize data for car #1 ---
    access.car = "Ford Fusion";
    access.year = 2006;
    access.mpg = 28.5;        
    hashMap.Insert("Kenneth",access);            
    
    // --- initialize data for car #2 ---
    access.car = "BMW 535i";
    access.year = 2014;
    access.mpg = 25.4;
    hashMap.Insert("Kenneth",access);
    
    // --- initialize data for car #3 ---
    access.car = "Nissan Altima";
    access.year = 2011;
    access.mpg = 30.7;
    hashMap.Insert("Jessica",access);     
    
    // --- initialize data for car #4 ---
    access.car = "Acura Integra";
    access.year = 2001;
    access.mpg = 20.2;    
    hashMap.Insert("Kenneth",access);       
    
    
    // diplay how many cars "Kenneth" owns
    cout <<"'Kenneth' owns "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl;             
    
    // display all items in the hash map
    // NOTE: its possible for multiple different keys types
    //   to be placed into the same hash map bucket     
    cout<<"\nThese are all of the cars in the hash map: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            // initialize an iterator
            iterDec iter = hashMap.begin(x);
            
            // display the key
            cout<<(*iter).key<<"'s car(s)\n";
            // display all the values 
            for(;iter != hashMap.end(x); ++iter)
            {
                cout<<"\tCar: "<<iter->value.car
                    <<"\n\tYear: "<<iter->value.year
                    <<"\n\tMPG: "<<iter->value.mpg<<endl<<endl;                                
            }
        }        
    }               
    
    // display the number of items in the hash map
    cout<<"The total number of cars in the hash map is: "<<
        hashMap.TotalElems()<<endl;   
    
    // sort the cars that "Kenneth" owns by name
    cout<<"\nSorting the cars that 'Kenneth' owns by name.. \n";         
    hashMap.Sort(hashMap.Hash("Kenneth"));    
    
    // display all items in the hash map again  
    cout<<"\nAgain, these are all of the cars in the hash map: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            // initialize an iterator
            iterDec iter = hashMap.begin(x);
            
            // display the key
            cout<<iter->key<<"'s car(s)\n";
            // display all the values 
            for(;iter != hashMap.end(x); ++iter)
            {
                cout<<"\tCar: "<<(*iter).value.car
                    <<"\n\tYear: "<<(*iter).value.year
                    <<"\n\tMPG: "<<(*iter).value.mpg<<endl<<endl;                
            }
        }        
    } 
 
    // remove the car 'Acura Integra' from "Kenneth's" inventory
    for(iterDec iter = hashMap.begin(hashMap.Hash("Kenneth")); 
        iter != hashMap.end(hashMap.Hash("Kenneth")); ++iter)
    {		
        if(iter->value.car == "Acura Integra")
        {
            cout<<"'"<<iter->value.car<<"' has been removed from 'Kenneth's' inventory..\n";
            hashMap.Remove("Kenneth",(*iter).value);
            break;
        }
    }    
    
    // display how many cars "Kenneth" owns
    cout <<"\n'Kenneth' now owns only "<<hashMap.ContainsKey("Kenneth")<<" cars"<<endl;                 
    
    // display all items in the hash map one more time  
    cout<<"\nThese are all of the cars in the hash map with the 'Acura Integra' removed: \n";
    for(int x=0; x < hashMap.TableSize(); ++x)
    {
        if(!hashMap.IsEmpty(x))
        {
            // initialize an iterator
            iterDec iter = hashMap.begin(x);
            
            // display the key
            cout<<(*iter).key<<"'s car(s)\n";
            // display all the values 
            for(;iter != hashMap.end(x); ++iter)
            {
                cout<<"\tCar: "<<iter->value.car
                    <<"\n\tYear: "<<iter->value.year
                    <<"\n\tMPG: "<<iter->value.mpg<<endl<<endl;
            }
        }        
    }     
    
    // display the number of items in the hash map
    cout<<"The total number of cars in the hash map is: "<<
        hashMap.TotalElems()<<endl;               
    
    return 0;
}// http://programmingnotes.org/

SAMPLE OUTPUT:

'Kenneth' owns 3 cars
These are all of the cars in the hash map: Jessica's car(s) Car: Nissan Altima Year: 2011 MPG: 30.7 Kenneth's car(s) Car: Ford Fusion Year: 2006 MPG: 28.5 Car: BMW 535i Year: 2014 MPG: 25.4 Car: Acura Integra Year: 2001 MPG: 20.2 ----------------------------------------------------- The total number of cars in the hash map is: 4 Sorting the cars that 'Kenneth' owns by name.. Again, these are all of the cars in the hash map: Jessica's car(s) Car: Nissan Altima Year: 2011 MPG: 30.7 Kenneth's car(s) Car: Acura Integra Year: 2001 MPG: 20.2 Car: BMW 535i Year: 2014 MPG: 25.4 Car: Ford Fusion Year: 2006 MPG: 28.5 ----------------------------------------------------- 'Acura Integra' has been removed from 'Kenneth's' inventory.. 'Kenneth' now owns only 2 cars These are all of the cars in the hash map with the 'Acura Integra' removed: Jessica's car(s) Car: Nissan Altima Year: 2011 MPG: 30.7 Kenneth's car(s) Car: BMW 535i Year: 2014 MPG: 25.4 Car: Ford Fusion Year: 2006 MPG: 28.5 -----------------------------------------------------
The total number of cars in the hash map is: 3

C++ || Custom Template Hash Table With Iterator Using Separate Chaining

January 18, 2013 admin No comments

Looking for sample code for a Hash Map? Click here!

Before we get into the code, what is a Hash Table? Simply put, a Hash Table is a data structure used to implement an associative array; one that can map unique “keys” to specific values. While a standard array requires that indice subscripts be integers, a hash table can use a floating point value, a string, another array, or even a structure as the index. That index is called the “key,” and the contents within the array at that specific index location is called the value. A hash table uses a hash function to generate an index into the table, creating buckets or slots, from which the correct value can be found.

To illustrate, compare a standard array full of data (100 elements). If the position was known for the specific item that we wanted to access within the array, we could quickly access it. For example, if we wanted to access the data located at index #5 in the array, we could access it by doing:

array[5]; // do something with the data

Here, we dont have to search through each element in the array to find what we need, we just access it at index #5. The question is, how do we know that index #5 stores the data that we are looking for? If we have a large set of data, doing a sequential search over each item within the array can be very inefficient. That is where hashing comes in handy. Given a “key,” we can apply a hash function to a unique index or bucket to find the data that we wish to access.

So in essence, a hash table is a data structure that stores key/value pairs, and is typically used because they are ideal for doing a quick search of items.

Though hashing is ideal, it isnt perfect. It is possible for multiple items to be hashed into the same location. Hash “collisions” are practically unavoidable when hashing large data sets. The code demonstrated on this page handles collisions via separate chaining, utilizing an array of linked list head nodes to store multiple values within one bucket – should any collisions occur.

An iterator was also implemented, making data access that much more simple within the hash table class. Click here for an overview demonstrating how custom iterators can be built.

Looking for sample code for a Hash Map? Click here!

=== CUSTOM TEMPLATE HASH TABLE WITH ITERATOR ===





		
		
			#include 'HashTable.h' - Hash Table With Iterator
			
C++
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Jan 18, 2013
//    Taken From: http://programmingnotes.org/
//    File:  HashTable.h
//    Description: This is a class which implements various functions which
//          demonstrates the use of a Hash Table.
// ============================================================================
#ifndef TEMPLATE_HASH_TABLE
#define TEMPLATE_HASH_TABLE
#include <iostream>
#include <string>
#include <sstream>
#include <cstdlib>

// if user doesnt define, this is the
// default hash table size
const int HASH_SIZE = 100;

template <class ItemType>
class HashTable
{
public:
    HashTable(int hashSze = HASH_SIZE);
        /*   Function: Constructor initializes hash table
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty(int key);
        /*   Function: Determines whether hash table is empty at the given key
            Precondition: Hash table has been created
            Postcondition: The function = true if the hash table is empty and the
                             function = false if hash table is not empty */
    bool  IsFull();
        /*   Function: Determines whether hash table is full
            Precondition: Hash table has been created
            Postcondition: The function = true if the hash table is full and the
                             function = false if hash table is not full */
    int Hash(ItemType newItem);
        /*   Function: Computes and returns a unique hash key for a given item
                        The returned key is the given cell where the item resides
            Precondition:  Hash table has been created and is not full
            Postcondition: The hash key is returned */
    void Insert(ItemType newItem);
        /*   Function: Adds newItem to the back of the list at a given key in the hash table
                         A unique hash key is automatically generated for each newItem
            Precondition:  Hash table has been created and is not full
            Postcondition: Item is in the hash table */
    void Append(int key, ItemType newItem);
        /*   Function: Adds new item to the end of the list at a given
                         key in the hash table
            Precondition:  Hash table has been created and is not full
            Postcondition: Item is in the hash table */
    bool Remove(ItemType deleteItem, int key = -1);
        /*   Function: Removes the first instance from the table whose value is "deleteItem"
                      Optional second parameter indicates the key where deleteItem is located
            Precondition:  Hash table has been created and is not empty
            Postcondition: The function = true if deleteItem is found and the
                             function = false if deleteItem is not found */
    void Sort(int key);
        /*   Function: Sort the items in the table at the given key
            Precondition: Hash table has been initialized
            Postcondition: The hash table is sorted */
    int TableSize();
        /*   Function: Return the size of the hash table
            Precondition: Hash table has been initialized
            Postcondition: The size of the hash table is returned */
    int TotalElems();
        /*   Function: Return the total number of elements contained in the hash table
            Precondition: Hash table has been initialized
            Postcondition: The size of the hash table is returned */
    int BucketSize(int key);
        /*   Function: Return the number of items contained in the hash table
                        cell at the given key
            Precondition: Hash table has been initialized
            Postcondition: The size of the given key cell is returned */
    int Count(ItemType searchItem);
        /*   Function: Return the number of times searchItem appears in the table.
                        Only works on items located in their correctly hashed cells
            Precondition: Hash table has been initialized
            Postcondition: The number of times searchItem appears in the table is returned */
    void MakeEmpty();
        /*   Function: Initializes hash table to an empty state
            Precondition: Hash table has been created
            Postcondition: Hash table no longer exists */
    ~HashTable();
        /*   Function: Removes the hash table
            Precondition: Hash table has been declared
            Postcondition: Hash table no longer exists */

    //  -- ITERATOR CLASS --
    class Iterator;
        /*   Function: Class declaration to the iterator
            Precondition: Hash table has been declared
            Postcondition: Hash Iterator has been declared */

    Iterator begin(int key){return(!IsEmpty(key)) ? head[key]:NULL;}
        /*   Function: Returns the beginning of the current hash cell list
            Precondition: Hash table has been declared
            Postcondition: Hash cell has been returned to the Iterator */

    Iterator end(int key=0){return NULL;}
        /*   Function: Returns the end of the current hash cell list
            Precondition: Hash table has been declared
            Postcondition: Hash cell has been returned to the Iterator */

private:
    struct node
    {
        ItemType currentItem;
        node* next;
    };
    node** head; // array of linked list declaration - front of each hash table cell
    int hashSize; // the size of the hash table (how many cells it has)
    int totElems; // holds the total number of elements in the entire table
    int* bucketSize; // holds the total number of elems in each specific hash table cell
};

//=========================  Implementation  ================================//

template<class ItemType>
HashTable<ItemType>::HashTable(int hashSze)
{
    hashSize = hashSze;
    head = new node*[hashSize];
    bucketSize = new int[hashSize];
    for(int x=0; x < hashSize; ++x)
    {
        head[x] = NULL;
        bucketSize[x] = 0;
    }
    totElems = 0;
}/* End of HashTable */

template<class ItemType>
bool HashTable<ItemType>::IsEmpty(int key)
{
    if(key >=0 && key < hashSize)
    {
        return head[key] == NULL;
    }
    return true;
}/* End of IsEmpty */

template<class ItemType>
bool HashTable<ItemType>::IsFull()
{
    try
    {
        node* location = new node;
        delete location;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}/* End of IsFull */

template<class ItemType>
int HashTable<ItemType>::Hash(ItemType newItem)
{
    long h = 19937;
    std::stringstream convert;

    // convert the parameter to a string using "stringstream" which is done
    // so we can hash multiple datatypes using only one function
    convert << newItem;
    std::string temp = convert.str();

    for(unsigned x=0; x < temp.length(); ++x)
    {
        h = (h << 6) ^ (h >> 26) ^ temp[x];
    }
    return abs(h % hashSize);
} /* End of Hash */

template<class ItemType>
void HashTable<ItemType>::Insert(ItemType newItem)
{
    if(IsFull())
    {
        //std::cout<<"nINSERT ERROR - HASH TABLE FULLn";
    }
    else
    {
        int key = Hash(newItem);
        Append(key,newItem);
    }
}/* End of Insert */

template<class ItemType>
void HashTable<ItemType>::Append(int key, ItemType newItem)
{
    if(IsFull())
    {
        //std::cout<<"nAPPEND ERROR - HASH TABLE FULLn";
    }
    else
    {
        node* newNode = new node;  // adds new node
        newNode-> currentItem = newItem;
        newNode-> next = NULL;

        if(IsEmpty(key))
        {
            head[key] = newNode;
        }
        else
        {
            node* tempPtr = head[key];
            while(tempPtr-> next != NULL)
            {
                tempPtr = tempPtr-> next;
            }
            tempPtr-> next = newNode;
        }
        ++bucketSize[key];
        ++totElems;
    }
}/* End of Append */

template<class ItemType>
bool HashTable<ItemType>::Remove(ItemType deleteItem, int key)
{
    bool isFound = false;
    node* tempPtr;
    if(key == -1)
    {
        key = Hash(deleteItem);
    }

    if(IsEmpty(key))
    {
        //std::cout<<"nREMOVE ERROR - HASH TABLE EMPTYn";
    }
    else if(head[key]->currentItem == deleteItem)
    {
        tempPtr = head[key];
        head[key] = head[key]-> next;
        delete tempPtr;
        --totElems;
        --bucketSize[key];
        isFound = true;
    }
    else
    {
        for(tempPtr = head[key];tempPtr->next!=NULL;tempPtr=tempPtr->next)
        {
            if(tempPtr->next->currentItem == deleteItem)
            {
                node* deleteNode = tempPtr->next;
                tempPtr-> next = tempPtr-> next-> next;
                delete deleteNode;
                isFound = true;
                --totElems;
                --bucketSize[key];
                break;
            }
        }
    }
    return isFound;
}/* End of Remove */

template<class ItemType>
void HashTable<ItemType>::Sort(int key)
{
    if(IsEmpty(key))
    {
        //std::cout<<"nSORT ERROR - HASH TABLE EMPTYn";
    }
    else
    {
        int listSize = BucketSize(key);
        bool sorted = false;

        do{
            sorted = true;
            int x = 0;
            for(node* tempPtr = head[key];
                tempPtr->next!=NULL && x < listSize-1;
                tempPtr=tempPtr->next,++x)
            {
                if(tempPtr-> currentItem > tempPtr->next->currentItem)
                {
                    ItemType temp = tempPtr-> currentItem;
                    tempPtr-> currentItem = tempPtr->next->currentItem;
                    tempPtr->next->currentItem = temp;
                    sorted = false;
                }
            }
            --listSize;
        }while(!sorted);
    }
}/* End of Sort */

template<class ItemType>
int HashTable<ItemType>::TableSize()
{
    return hashSize;
}/* End of TableSize */

template<class ItemType>
int HashTable<ItemType>::TotalElems()
{
    return totElems;
}/* End of TotalElems */

template<class ItemType>
int HashTable<ItemType>::BucketSize(int key)
{
    return(!IsEmpty(key)) ? bucketSize[key]:0;
}/* End of BucketSize */

template<class ItemType>
int HashTable<ItemType>::Count(ItemType searchItem)
{
    int key = Hash(searchItem);
    int search = 0;

    if(IsEmpty(key))
    {
        //std::cout<<"nCOUNT ERROR - HASH TABLE EMPTYn";
    }
    else
    {
        for(node* tempPtr = head[key];tempPtr!=NULL;tempPtr=tempPtr->next)
        {
            if(tempPtr->currentItem == searchItem)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of Count */

template<class ItemType>
void HashTable<ItemType>::MakeEmpty()
{
    totElems = 0;
    for(int x=0; x < hashSize; ++x)
    {
        if(!IsEmpty(x))
        {
            //std::cout << "Destroying nodes ...n";
            while(!IsEmpty(x))
            {
                node* temp = head[x];
                //std::cout << temp-> currentItem <<std::endl;
                head[x] = head[x]-> next;
                delete temp;
            }
        }
        bucketSize[x] = 0;
    }
}/* End of MakeEmpty */

template<class ItemType>
HashTable<ItemType>::~HashTable()
{
    MakeEmpty();
    delete[] head;
    delete[] bucketSize;
}/* End of ~HashTable */

//   END OF THE HASH TABLE CLASS
// -----------------------------------------------------------
//   START OF THE HASH TABLE ITERATOR CLASS

template <class ItemType>
class HashTable<ItemType>::Iterator :
        public std::iterator<std::forward_iterator_tag,ItemType>,
        public HashTable<ItemType>
    {
public:
    // Iterator constructor
    Iterator(node* otherIter = NULL)
    {
        itHead = otherIter;
    }
    ~Iterator() {}
    // The assignment and relational operators are straightforward
    Iterator& operator=(const Iterator& other)
    {
        itHead = other.itHead;
        return(*this);
    }
    bool operator==(const Iterator& other)const
    {
        return itHead == other.itHead;
    }
    bool operator!=(const Iterator& other)const
    {
        return itHead != other.itHead;
    }
    bool operator<(const Iterator& other)const
    {
        return itHead < other.itHead;
    }
    bool operator>(const Iterator& other)const
    {
        return other.itHead < itHead;
    }
    bool operator<=(const Iterator& other)const
    {
        return (!(other.itHead < itHead));
    }
    bool operator>=(const Iterator& other)const
    {
        return (!(itHead < other.itHead));
    }
    // Update my state such that I refer to the next element in the
    // HashTable.
    Iterator operator+(int incr)
    {
        node* temp = itHead;
        for(int x=0; x < incr && temp!= NULL; ++x)
        {
            temp = temp->next;
        }
        return temp;
    }
    Iterator operator+=(int incr)
    {
        for(int x=0; x < incr && itHead!= NULL; ++x)
        {
            itHead = itHead->next;
        }
        return itHead;
    }
    Iterator& operator++() // pre increment
    {
        if(itHead != NULL)
        {
            itHead = itHead->next;
        }
        return(*this);
    }
    Iterator operator++(int) // post increment
    {
        node* temp = itHead;
        this->operator++();
        return temp;
    }
    ItemType& operator[](int incr)
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL || (*this + incr) == NULL)
        {
            return junk;
        }
        return(*(*this + incr));
    }
    // Return a reference to the value in the node.  I do this instead
    // of returning by value so a caller can update the value in the
    // node directly.
    ItemType& operator*()
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL)
        {
            return junk;
        }
        return itHead->currentItem;
    }
    ItemType* operator->()
    {
        return(&**this);
    }
private:
    node* itHead;
    ItemType junk;
};
#endif // http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Jan 18, 2013
//    Taken From: http://programmingnotes.org/
//    File:  HashTable.h
//    Description: This is a class which implements various functions which
//          demonstrates the use of a Hash Table.
// ============================================================================
#ifndef TEMPLATE_HASH_TABLE
#define TEMPLATE_HASH_TABLE
#include <iostream>
#include <string>
#include <sstream>
#include <cstdlib>
 
// if user doesnt define, this is the
// default hash table size
const int HASH_SIZE = 100;
 
template <class ItemType>
class HashTable
{
public:
    HashTable(int hashSze = HASH_SIZE);
        /*   Function: Constructor initializes hash table
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty(int key);
        /*   Function: Determines whether hash table is empty at the given key
            Precondition: Hash table has been created
            Postcondition: The function = true if the hash table is empty and the
                             function = false if hash table is not empty */
    bool  IsFull();
        /*   Function: Determines whether hash table is full
            Precondition: Hash table has been created
            Postcondition: The function = true if the hash table is full and the
                             function = false if hash table is not full */
    int Hash(ItemType newItem);
        /*   Function: Computes and returns a unique hash key for a given item
                        The returned key is the given cell where the item resides
            Precondition:  Hash table has been created and is not full
            Postcondition: The hash key is returned */
    void Insert(ItemType newItem);
        /*   Function: Adds newItem to the back of the list at a given key in the hash table
                         A unique hash key is automatically generated for each newItem
            Precondition:  Hash table has been created and is not full
            Postcondition: Item is in the hash table */
    void Append(int key, ItemType newItem);
        /*   Function: Adds new item to the end of the list at a given
                         key in the hash table
            Precondition:  Hash table has been created and is not full
            Postcondition: Item is in the hash table */
    bool Remove(ItemType deleteItem, int key = -1);
        /*   Function: Removes the first instance from the table whose value is "deleteItem"
                      Optional second parameter indicates the key where deleteItem is located
            Precondition:  Hash table has been created and is not empty
            Postcondition: The function = true if deleteItem is found and the
                             function = false if deleteItem is not found */
    void Sort(int key);
        /*   Function: Sort the items in the table at the given key
            Precondition: Hash table has been initialized
            Postcondition: The hash table is sorted */
    int TableSize();
        /*   Function: Return the size of the hash table
            Precondition: Hash table has been initialized
            Postcondition: The size of the hash table is returned */
    int TotalElems();
        /*   Function: Return the total number of elements contained in the hash table
            Precondition: Hash table has been initialized
            Postcondition: The size of the hash table is returned */
    int BucketSize(int key);
        /*   Function: Return the number of items contained in the hash table
                        cell at the given key
            Precondition: Hash table has been initialized
            Postcondition: The size of the given key cell is returned */
    int Count(ItemType searchItem);
        /*   Function: Return the number of times searchItem appears in the table.
                        Only works on items located in their correctly hashed cells
            Precondition: Hash table has been initialized
            Postcondition: The number of times searchItem appears in the table is returned */
    void MakeEmpty();
        /*   Function: Initializes hash table to an empty state
            Precondition: Hash table has been created
            Postcondition: Hash table no longer exists */
    ~HashTable();
        /*   Function: Removes the hash table
            Precondition: Hash table has been declared
            Postcondition: Hash table no longer exists */
 
    //  -- ITERATOR CLASS --
    class Iterator;
        /*   Function: Class declaration to the iterator
            Precondition: Hash table has been declared
            Postcondition: Hash Iterator has been declared */
 
    Iterator begin(int key){return(!IsEmpty(key)) ? head[key]:NULL;}
        /*   Function: Returns the beginning of the current hash cell list
            Precondition: Hash table has been declared
            Postcondition: Hash cell has been returned to the Iterator */
 
    Iterator end(int key=0){return NULL;}
        /*   Function: Returns the end of the current hash cell list
            Precondition: Hash table has been declared
            Postcondition: Hash cell has been returned to the Iterator */
 
private:
    struct node
    {
        ItemType currentItem;
        node* next;
    };
    node** head; // array of linked list declaration - front of each hash table cell
    int hashSize; // the size of the hash table (how many cells it has)
    int totElems; // holds the total number of elements in the entire table
    int* bucketSize; // holds the total number of elems in each specific hash table cell
};
 
//=========================  Implementation  ================================//
 
template<class ItemType>
HashTable<ItemType>::HashTable(int hashSze)
{
    hashSize = hashSze;
    head = new node*[hashSize];
    bucketSize = new int[hashSize];
    for(int x=0; x < hashSize; ++x)
    {
        head[x] = NULL;
        bucketSize[x] = 0;
    }
    totElems = 0;
}/* End of HashTable */
 
template<class ItemType>
bool HashTable<ItemType>::IsEmpty(int key)
{
    if(key >=0 && key < hashSize)
    {
        return head[key] == NULL;
    }
    return true;
}/* End of IsEmpty */
 
template<class ItemType>
bool HashTable<ItemType>::IsFull()
{
    try
    {
        node* location = new node;
        delete location;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}/* End of IsFull */
 
template<class ItemType>
int HashTable<ItemType>::Hash(ItemType newItem)
{
    long h = 19937;
    std::stringstream convert;
 
    // convert the parameter to a string using "stringstream" which is done
    // so we can hash multiple datatypes using only one function
    convert << newItem;
    std::string temp = convert.str();
 
    for(unsigned x=0; x < temp.length(); ++x)
    {
        h = (h << 6) ^ (h >> 26) ^ temp[x];
    }
    return abs(h % hashSize);
} /* End of Hash */
 
template<class ItemType>
void HashTable<ItemType>::Insert(ItemType newItem)
{
    if(IsFull())
    {
        //std::cout<<"nINSERT ERROR - HASH TABLE FULLn";
    }
    else
    {
        int key = Hash(newItem);
        Append(key,newItem);
    }
}/* End of Insert */
 
template<class ItemType>
void HashTable<ItemType>::Append(int key, ItemType newItem)
{
    if(IsFull())
    {
        //std::cout<<"nAPPEND ERROR - HASH TABLE FULLn";
    }
    else
    {
        node* newNode = new node;  // adds new node
        newNode-> currentItem = newItem;
        newNode-> next = NULL;
 
        if(IsEmpty(key))
        {
            head[key] = newNode;
        }
        else
        {
            node* tempPtr = head[key];
            while(tempPtr-> next != NULL)
            {
                tempPtr = tempPtr-> next;
            }
            tempPtr-> next = newNode;
        }
        ++bucketSize[key];
        ++totElems;
    }
}/* End of Append */
 
template<class ItemType>
bool HashTable<ItemType>::Remove(ItemType deleteItem, int key)
{
    bool isFound = false;
    node* tempPtr;
    if(key == -1)
    {
        key = Hash(deleteItem);
    }
 
    if(IsEmpty(key))
    {
        //std::cout<<"nREMOVE ERROR - HASH TABLE EMPTYn";
    }
    else if(head[key]->currentItem == deleteItem)
    {
        tempPtr = head[key];
        head[key] = head[key]-> next;
        delete tempPtr;
        --totElems;
        --bucketSize[key];
        isFound = true;
    }
    else
    {
        for(tempPtr = head[key];tempPtr->next!=NULL;tempPtr=tempPtr->next)
        {
            if(tempPtr->next->currentItem == deleteItem)
            {
                node* deleteNode = tempPtr->next;
                tempPtr-> next = tempPtr-> next-> next;
                delete deleteNode;
                isFound = true;
                --totElems;
                --bucketSize[key];
                break;
            }
        }
    }
    return isFound;
}/* End of Remove */
 
template<class ItemType>
void HashTable<ItemType>::Sort(int key)
{
    if(IsEmpty(key))
    {
        //std::cout<<"nSORT ERROR - HASH TABLE EMPTYn";
    }
    else
    {
        int listSize = BucketSize(key);
        bool sorted = false;
 
        do{
            sorted = true;
            int x = 0;
            for(node* tempPtr = head[key];
                tempPtr->next!=NULL && x < listSize-1;
                tempPtr=tempPtr->next,++x)
            {
                if(tempPtr-> currentItem > tempPtr->next->currentItem)
                {
                    ItemType temp = tempPtr-> currentItem;
                    tempPtr-> currentItem = tempPtr->next->currentItem;
                    tempPtr->next->currentItem = temp;
                    sorted = false;
                }
            }
            --listSize;
        }while(!sorted);
    }
}/* End of Sort */
 
template<class ItemType>
int HashTable<ItemType>::TableSize()
{
    return hashSize;
}/* End of TableSize */
 
template<class ItemType>
int HashTable<ItemType>::TotalElems()
{
    return totElems;
}/* End of TotalElems */
 
template<class ItemType>
int HashTable<ItemType>::BucketSize(int key)
{
    return(!IsEmpty(key)) ? bucketSize[key]:0;
}/* End of BucketSize */
 
template<class ItemType>
int HashTable<ItemType>::Count(ItemType searchItem)
{
    int key = Hash(searchItem);
    int search = 0;
 
    if(IsEmpty(key))
    {
        //std::cout<<"nCOUNT ERROR - HASH TABLE EMPTYn";
    }
    else
    {
        for(node* tempPtr = head[key];tempPtr!=NULL;tempPtr=tempPtr->next)
        {
            if(tempPtr->currentItem == searchItem)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of Count */
 
template<class ItemType>
void HashTable<ItemType>::MakeEmpty()
{
    totElems = 0;
    for(int x=0; x < hashSize; ++x)
    {
        if(!IsEmpty(x))
        {
            //std::cout << "Destroying nodes ...n";
            while(!IsEmpty(x))
            {
                node* temp = head[x];
                //std::cout << temp-> currentItem <<std::endl;
                head[x] = head[x]-> next;
                delete temp;
            }
        }
        bucketSize[x] = 0;
    }
}/* End of MakeEmpty */
 
template<class ItemType>
HashTable<ItemType>::~HashTable()
{
    MakeEmpty();
    delete[] head;
    delete[] bucketSize;
}/* End of ~HashTable */
 
//   END OF THE HASH TABLE CLASS
// -----------------------------------------------------------
//   START OF THE HASH TABLE ITERATOR CLASS
 
template <class ItemType>
class HashTable<ItemType>::Iterator :
        public std::iterator<std::forward_iterator_tag,ItemType>,
        public HashTable<ItemType>
    {
public:
    // Iterator constructor
    Iterator(node* otherIter = NULL)
    {
        itHead = otherIter;
    }
    ~Iterator() {}
    // The assignment and relational operators are straightforward
    Iterator& operator=(const Iterator& other)
    {
        itHead = other.itHead;
        return(*this);
    }
    bool operator==(const Iterator& other)const
    {
        return itHead == other.itHead;
    }
    bool operator!=(const Iterator& other)const
    {
        return itHead != other.itHead;
    }
    bool operator<(const Iterator& other)const
    {
        return itHead < other.itHead;
    }
    bool operator>(const Iterator& other)const
    {
        return other.itHead < itHead;
    }
    bool operator<=(const Iterator& other)const
    {
        return (!(other.itHead < itHead));
    }
    bool operator>=(const Iterator& other)const
    {
        return (!(itHead < other.itHead));
    }
    // Update my state such that I refer to the next element in the
    // HashTable.
    Iterator operator+(int incr)
    {
        node* temp = itHead;
        for(int x=0; x < incr && temp!= NULL; ++x)
        {
            temp = temp->next;
        }
        return temp;
    }
    Iterator operator+=(int incr)
    {
        for(int x=0; x < incr && itHead!= NULL; ++x)
        {
            itHead = itHead->next;
        }
        return itHead;
    }
    Iterator& operator++() // pre increment
    {
        if(itHead != NULL)
        {
            itHead = itHead->next;
        }
        return(*this);
    }
    Iterator operator++(int) // post increment
    {
        node* temp = itHead;
        this->operator++();
        return temp;
    }
    ItemType& operator[](int incr)
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL || (*this + incr) == NULL)
        {
            return junk;
        }
        return(*(*this + incr));
    }
    // Return a reference to the value in the node.  I do this instead
    // of returning by value so a caller can update the value in the
    // node directly.
    ItemType& operator*()
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL)
        {
            return junk;
        }
        return itHead->currentItem;
    }
    ItemType* operator->()
    {
        return(&**this);
    }
private:
    node* itHead;
    ItemType junk;
};
#endif // http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The iterator class starts on line #368, and is built to support most of the standard relational operators, as well as arithmetic operators such as ‘+,+=,++’ (pre/post increment). The * (star), bracket [] and -> arrow operators are also supported. Click here for an overview demonstrating how custom iterators can be built.

The rest of the code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Looking for sample code for a Hash Map? Click here!

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as many of its STL template class counterparts. Here are sample programs demonstrating its use.





		
		
			#1 - Demonstrate Basic Use
			
C++
			
			// DEMONSTRATE USE OF THE REMOVE AND SORT FUNCTIONS
#include <iostream>
#include <ctime>
#include <string>
#include <cstdlib>
#include <iomanip>
#include "HashTable.h"
using namespace std;

// iterator declarations
typedef HashTable<string>::Iterator strIterDec;

// hash table size
const int TABLE_SIZE = 5;

int main()
{
	// delcare variables
	srand(time(NULL));
	const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",
        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",
        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",
        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",
        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",
        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",
        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",
        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",
        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",
        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",
        "Kenneth","Perkins","Kaleena"};

	int nameLen = sizeof(names)/sizeof(names[0]); 

	// Hash table class declarations
	HashTable<string> strHash(TABLE_SIZE);

	// insert 10 items into each hash table
	for(int x=0; x < (TABLE_SIZE*2); ++x)
	{
		// place all data in bucket 0
		// NOTE: you dont want to place all data into one
		// bucket, this is done for demo purposes only
		// Normally use the "Insert" function instead
		strHash.Append(0,names[rand()%(nameLen-1)]);
	}

	// assign the iterator to bucket 0
	strIterDec it = strHash.begin(0);

	// display bucket size
	cout<<"Bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl;

	// display the first item
	cout<<"The first element in bucket #0 is "<< it[0] <<endl;	

	// remove the first item in bucket 0
	// NOTE: the second parameter is optional
	// but since we know we want bucket 0, we use it here
	strHash.Remove(it[0],0);

	// update the iterator to the new table state
	it = strHash.begin(0);

	// display the new first item	
	cout<<"nNow bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl;
	cout<<"The first element in bucket #0 is "<< it[0] <<endl;

	// display all the items within the "strHash" table
	cout<<"nThe unsorted items in strHash bucket #0:n";
	for(int x=0; x < strHash.BucketSize(0); ++x)
	{		
		cout << "it[] = " << it[x] << endl;
	}

	// sort the items in bucket 0
	strHash.Sort(0);

	// display all the items within the "strHash" table
	cout<<"nThe sorted items in strHash bucket #0:n";
	for(int x=0; x < strHash.BucketSize(0); ++x)
	{		
		cout << "it[] = " << it[x] << endl;
	}

	return 0;
}// http://programmingnotes.org/
			
				
					
				
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						// DEMONSTRATE USE OF THE REMOVE AND SORT FUNCTIONS
#include <iostream>
#include <ctime>
#include <string>
#include <cstdlib>
#include <iomanip>
#include "HashTable.h"
using namespace std;
 
// iterator declarations
typedef HashTable<string>::Iterator strIterDec;
 
// hash table size
const int TABLE_SIZE = 5;
 
int main()
{
	// delcare variables
	srand(time(NULL));
	const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",
        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",
        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",
        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",
        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",
        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",
        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",
        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",
        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",
        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",
        "Kenneth","Perkins","Kaleena"};
 
	int nameLen = sizeof(names)/sizeof(names[0]); 
 
	// Hash table class declarations
	HashTable<string> strHash(TABLE_SIZE);
 
	// insert 10 items into each hash table
	for(int x=0; x < (TABLE_SIZE*2); ++x)
	{
		// place all data in bucket 0
		// NOTE: you dont want to place all data into one
		// bucket, this is done for demo purposes only
		// Normally use the "Insert" function instead
		strHash.Append(0,names[rand()%(nameLen-1)]);
	}
 
	// assign the iterator to bucket 0
	strIterDec it = strHash.begin(0);
 
	// display bucket size
	cout<<"Bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl;
 
	// display the first item
	cout<<"The first element in bucket #0 is "<< it[0] <<endl;	
 
	// remove the first item in bucket 0
	// NOTE: the second parameter is optional
	// but since we know we want bucket 0, we use it here
	strHash.Remove(it[0],0);
 
	// update the iterator to the new table state
	it = strHash.begin(0);
 
	// display the new first item	
	cout<<"nNow bucket #0 has "<<strHash.BucketSize(0)<<" items"<<endl;
	cout<<"The first element in bucket #0 is "<< it[0] <<endl;
 
	// display all the items within the "strHash" table
	cout<<"nThe unsorted items in strHash bucket #0:n";
	for(int x=0; x < strHash.BucketSize(0); ++x)
	{		
		cout << "it[] = " << it[x] << endl;
	}
 
	// sort the items in bucket 0
	strHash.Sort(0);
 
	// display all the items within the "strHash" table
	cout<<"nThe sorted items in strHash bucket #0:n";
	for(int x=0; x < strHash.BucketSize(0); ++x)
	{		
		cout << "it[] = " << it[x] << endl;
	}
 
	return 0;
}// http://programmingnotes.org/

SAMPLE OUTPUT:

Bucket #0 has 10 items The first element in bucket #0 is Homer
Now bucket #0 has 9 items The first element in bucket #0 is Tamra The unsorted items in strHash bucket #0: it[] = Tamra it[] = Lyndon it[] = Johanna it[] = Perkins it[] = Alva it[] = Jordon it[] = Neville it[] = Lawrence it[] = Jetta
The sorted items in strHash bucket #0: it[] = Alva it[] = Jetta it[] = Johanna it[] = Jordon it[] = Lawrence it[] = Lyndon it[] = Neville it[] = Perkins it[] = Tamra





		
		
			#2 - Display Items
			
C++
			
			// DISPLAY ALL DATA INSIDE TABLE USING STD::STRING / INT / STRUCT
#include <iostream>
#include <ctime>
#include <string>
#include <cstdlib>
#include <iomanip>
#include "HashTable.h"
using namespace std;

// sample struct demo
struct MyStruct
{
	string name;
};

// iterator declarations
typedef HashTable<string>::Iterator strIterDec;
typedef HashTable<int>::Iterator intIterDec;
typedef HashTable<MyStruct>::Iterator strctIterDec;

// hash table size
const int TABLE_SIZE = 10;

int main()
{
	// delcare variables
	srand(time(NULL));
	const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",
        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",
        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",
        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",
        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",
        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",
        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",
        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",
        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",
        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",
        "Kenneth","Perkins","Kaleena"};
     
	int nameLen = sizeof(names)/sizeof(names[0]); 

	// Hash table class declarations
	HashTable<string> strHash(TABLE_SIZE);
	HashTable<int> intHash = TABLE_SIZE; 
	HashTable<MyStruct> strctHash = TABLE_SIZE;

	// access struct element
	MyStruct strctAccess;	

	// insert 20 items into each hash table
	for(int x=0; x < (TABLE_SIZE*2); ++x)
	{
		// Use the "insert" function to place data into the hash table
		// this function automatically hashes the basic datatypes
		// i.e: int, double, char, char*, string
		strHash.Insert(names[rand()%(nameLen-1)]);
		intHash.Insert(rand()%10000);

		// The "insert" function cant be used on a struct, so we
		// use the "append" function for the struct declaration.
		// We use the "strHash" class declaration to use its
		// hash function, then place the struct in an appropriate 
		// hashed bucket
		strctAccess.name = names[rand()%(nameLen-1)];
		int strctHashKey = strHash.Hash(strctAccess.name);		
		strctHash.Append(strctHashKey,strctAccess);
	}

	// display all the items within the "strHash" table
	for(int x=0; x < strHash.TableSize(); ++x)
	{
		if(!strHash.IsEmpty(x))
		{
			cout<<"nstrHash Bucket #"<<x<<":n";
			for(strIterDec it = strHash.begin(x); it != strHash.end(x); it+=1) 
			{
				// access elements using the * (star) operator
				cout << "*it = " << *it << endl;
			}
		}
	}
	// creates a line seperator
	cout<<endl;
	cout.fill('-');
	cout<<left<<setw(80)<<""<<endl;

	// display all the items within the "intHash" table
	for(int x=0; x < intHash.TableSize(); ++x)
	{		
		intIterDec it = intHash.begin(x);
		if(!intHash.IsEmpty(x))
		{
			cout<<"nintHash Bucket #"<<x<<":n";
			for(int y = 0; y < intHash.BucketSize(x); ++y) 
			{
				// access elements using the [] operator
				cout << "it[] = " << it[y] << endl;
			}
		}
	}

	// creates a line seperator
	cout<<endl;
	cout.fill('-');
	cout<<left<<setw(80)<<""<<endl;

	// display all the items within the "strctHash" table
	for(int x=0; x < strctHash.TableSize(); ++x)
	{				
		if(!strctHash.IsEmpty(x))
		{
			cout<<"nstrctHash Bucket #"<<x<<":n";
			for(strctIterDec it = strctHash.begin(x); it!=strctHash.end(x); it=it+1) 
			{
				// access struct/class elements using the -> operator
				cout << "it-> = " << it->name << endl;
			}
		}
	}

	return 0;
}// http://programmingnotes.org/
			
				
					
				
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						// DISPLAY ALL DATA INSIDE TABLE USING STD::STRING / INT / STRUCT
#include <iostream>
#include <ctime>
#include <string>
#include <cstdlib>
#include <iomanip>
#include "HashTable.h"
using namespace std;
 
// sample struct demo
struct MyStruct
{
	string name;
};
 
// iterator declarations
typedef HashTable<string>::Iterator strIterDec;
typedef HashTable<int>::Iterator intIterDec;
typedef HashTable<MyStruct>::Iterator strctIterDec;
 
// hash table size
const int TABLE_SIZE = 10;
 
int main()
{
	// delcare variables
	srand(time(NULL));
	const string names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",
        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",
        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",
        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",
        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",
        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",
        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",
        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",
        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",
        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",
        "Kenneth","Perkins","Kaleena"};
     
	int nameLen = sizeof(names)/sizeof(names[0]); 
 
	// Hash table class declarations
	HashTable<string> strHash(TABLE_SIZE);
	HashTable<int> intHash = TABLE_SIZE; 
	HashTable<MyStruct> strctHash = TABLE_SIZE;
 
	// access struct element
	MyStruct strctAccess;	
 
	// insert 20 items into each hash table
	for(int x=0; x < (TABLE_SIZE*2); ++x)
	{
		// Use the "insert" function to place data into the hash table
		// this function automatically hashes the basic datatypes
		// i.e: int, double, char, char*, string
		strHash.Insert(names[rand()%(nameLen-1)]);
		intHash.Insert(rand()%10000);
 
		// The "insert" function cant be used on a struct, so we
		// use the "append" function for the struct declaration.
		// We use the "strHash" class declaration to use its
		// hash function, then place the struct in an appropriate 
		// hashed bucket
		strctAccess.name = names[rand()%(nameLen-1)];
		int strctHashKey = strHash.Hash(strctAccess.name);		
		strctHash.Append(strctHashKey,strctAccess);
	}
 
	// display all the items within the "strHash" table
	for(int x=0; x < strHash.TableSize(); ++x)
	{
		if(!strHash.IsEmpty(x))
		{
			cout<<"nstrHash Bucket #"<<x<<":n";
			for(strIterDec it = strHash.begin(x); it != strHash.end(x); it+=1) 
			{
				// access elements using the * (star) operator
				cout << "*it = " << *it << endl;
			}
		}
	}
	// creates a line seperator
	cout<<endl;
	cout.fill('-');
	cout<<left<<setw(80)<<""<<endl;
 
	// display all the items within the "intHash" table
	for(int x=0; x < intHash.TableSize(); ++x)
	{		
		intIterDec it = intHash.begin(x);
		if(!intHash.IsEmpty(x))
		{
			cout<<"nintHash Bucket #"<<x<<":n";
			for(int y = 0; y < intHash.BucketSize(x); ++y) 
			{
				// access elements using the [] operator
				cout << "it[] = " << it[y] << endl;
			}
		}
	}
 
	// creates a line seperator
	cout<<endl;
	cout.fill('-');
	cout<<left<<setw(80)<<""<<endl;
 
	// display all the items within the "strctHash" table
	for(int x=0; x < strctHash.TableSize(); ++x)
	{				
		if(!strctHash.IsEmpty(x))
		{
			cout<<"nstrctHash Bucket #"<<x<<":n";
			for(strctIterDec it = strctHash.begin(x); it!=strctHash.end(x); it=it+1) 
			{
				// access struct/class elements using the -> operator
				cout << "it-> = " << it->name << endl;
			}
		}
	}
 
	return 0;
}// http://programmingnotes.org/

SAMPLE OUTPUT:

strHash Bucket #0: *it = Cinderella *it = Perkins *it = Krystal *it = Roger *it = Roger
strHash Bucket #1: *it = Lilliam *it = Lilliam *it = Theda strHash Bucket #2: *it = Arie strHash Bucket #3: *it = Magda strHash Bucket #6: *it = Edda *it = Irvin *it = Kati *it = Lyndon strHash Bucket #7: *it = Deb *it = Jaime strHash Bucket #8: *it = Neville *it = Victoria strHash Bucket #9: *it = Chery *it = Evelia -------------------------------------------- intHash Bucket #0: it[] = 2449 it[] = 6135 intHash Bucket #1: it[] = 1120 it[] = 852 intHash Bucket #2: it[] = 5727 intHash Bucket #3: it[] = 1174 intHash Bucket #4: it[] = 2775 it[] = 3525 it[] = 8375 intHash Bucket #5: it[] = 4322 it[] = 8722 it[] = 5016 intHash Bucket #6: it[] = 5053 it[] = 7231 it[] = 1571 intHash Bucket #7: it[] = 1666 it[] = 4510 it[] = 1548 it[] = 3646 intHash Bucket #9: it[] = 2756 -------------------------------------------- strctHash Bucket #0: it-> = Cherilyn it-> = Roger strctHash Bucket #1: it-> = Tamra it-> = Alex it-> = Theda strctHash Bucket #2: it-> = Nigel it-> = Alva it-> = Arie strctHash Bucket #4: it-> = Basil strctHash Bucket #5: it-> = Tod strctHash Bucket #6: it-> = Irvin it-> = Lyndon strctHash Bucket #7: it-> = Amina it-> = Hillary it-> = Kenneth it-> = Amina strctHash Bucket #8: it-> = Gene it-> = Lemuel it-> = Gene
strctHash Bucket #9: it-> = Albertina

Tag Archives: template class

C++ || Custom Template Hash Map With Iterator Using Separate Chaining

C++ || Custom Template Hash Table With Iterator Using Separate Chaining

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