Tag Archives: hash table
C++ || Multi Process Server & Client Hash Table Using Thread Pools, Message Queues, & Signal Handlers
The following is another homework assignment which was presented in an Operating Systems Concepts class. Using commandline arguments, the following is a program which implements a multi threaded hash table, utilizing message queues to pass text from a client program to a server program and vice versa. This program makes use of multiple interprocess communication function calls provided on Unix based systems.
REQUIRED KNOWLEDGE FOR THIS PROGRAM
How To Override The Default Signal Handler (CTRL-C)
How To Create And Use Pthreads For Interprocess Communication
How To Use Message Queues For Interprocess Communication
Multi Process Synchronization Producer Consumer Problem Using Pthreads
Sample Input Server Records File - Download Here
==== 1. OVERVIEW ====
Hash tables are widely used for efficient storage and retrieval of data. When using hash tables in multi threaded applications, you must ensure that concurrent accesses into the hash table is free from race conditions, dead locks, and other problems that arise in program synchronization.
One solution to overcome this problem is to prevent concurrent accesses into the hash table altogether; i.e. prior to accessing the hash table, a thread acquires a lock, and then releases the lock after the access is complete. Such approach, although simple, is inefficient. The program demonstrated on this page implements an alternative solution, one which permits safe concurrent accesses into the hash table. In the approach implemented on this page, each hash location within a hash table is protected with a separate lock. Hence, multiple threads access the hash table concurrently as long as they are accessing different hash locations. For greater efficiency, this program also makes use of a thread pool.
==== 2. TECHNICAL DETAILS ====
This program was implemented in two parts; a server program and a client program. The server side of the program maintains a hash table of records and a pool of threads. The client program requests from the server program search records by sending record ids over a message queue. The server program then retrieves a request from the message queue, and wakes up a thread in the thread pool. That awakened thread then uses the id (sent from the client program) to retrieve the corresponding record from the hash table, and sends the found record from the server program to the client program over the message queue.
The server also reads a specified file from the commandline, which stores initial user data that is to be inserted and stored into the hash table. The incoming text file has the following format:
a unique numerical id 1 (an integer)
the first name 1 (a string)
the last name 1 (a string)
.
.
.
a unique numerical id N (an integer)
the first name N (a string)
the last name N (a string)
These three fields make up one single record for one individual. More than one record may be present in the incoming text file.
==== 3. SERVER ====
The server has the following structure and function:
The server program is invoked with the following commandline structure:
./Server [FILE NAME] [NUMBER OF THREADS] (e.g. ./Server database.dat 10)
The server is implemented below.
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// ============================================================================= // Author: K Perkins // Date: Oct 5, 2013 // Taken From: http://programmingnotes.org/ // File: Server.cpp // Description: Using a Hash Table, this program simulates a server and client // application. The server program maintains a hash table of records and // a pool of threads. The client requests records from the server by sending // record ID's over the message queue. The server retrieves a request from // the message queue and wakes up a thread in the thread pool. The awakened // thread then uses the ID to retrieve the corresponding record from the // hash table and sends the record to the client over the message queue. // // This is the server program which creates a message queue using the msgget() // system call, checks the message queue for new messages using the msgrcv() // system call, and uses the msgsnd system call to send messages back to // the client // ============================================================================= #include <iostream> #include <vector> #include <list> #include <cstdlib> #include <cstring> #include <fstream> #include <csignal> #include <pthread.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #include <unistd.h> using namespace std; // Compile & Run // g++ Server.cpp -o Server -lpthread // ./Server <FILE NAME> <NUMBER OF THREADS> // function prototypes void SignalHandler(int arg); void InsertInitialDataIntoTable(ifstream& infile); void* SearchRecords(void* args); void SendRecord(int id, const char* firstName, const char* lastName); void* GenerateNewRecord(void* args); // items which are placed inside the hash table cell struct Record { int id; char firstName[50]; char lastName[50]; }; // cell for the hash table struct Cell { list<Record> cell; pthread_mutex_t mutex; }; // message queue structure struct MsgQueue { // the channel the connection will be on long messageType; int recordID; char recordName[100]; }; // constant variables const int HASH_TABLE_SIZE = 100; const int NUM_NEW_RECORDS_THREADS = 5; const int CLIENT_TO_SERVER_CHANNEL = 2; const int SERVER_TO_CLIENT_CHANNEL = 4; const int MSG_Q_ID = 0664; // global variables int msqid = 0; // message queue ID vector<Cell> hashTable(HASH_TABLE_SIZE); list<int> recievedMsg; int main(int argc, char* argv[]) { // declare variables srand(time(NULL)); signal(SIGINT, SignalHandler); // override the CTRL-C terminal singal ifstream infile; // used to read in the file int searchThreadNum = 0; // keep track of how many threads are being processed int newRecThreadNum = 0; int numSearchThreads = 0; // how many threads search the table for records key_t key = 0; // generate key to a file pthread_t* searchRecordThreads = NULL; // array of search records threads pthread_t* getNewRecordThreads = NULL; // array of new records threads MsgQueue msg; // instantiate a message queue // check if theres enough commandline args if(argc < 3) { cerr<<"n** ERROR NOT ENOUGH ARGS!nn" <<"USAGE: "<<argv[0]<<" <FILE NAME> <NUMBER OF THREADS>nn"; exit(1); } // open the input records file infile.open(argv[1]); // check to see if file exists if(infile.fail()) { cerr<<"n** ERROR: ""<<argv[1]<<"" could not be found!n"; exit(1); } // insert data into the hash table from the source file InsertInitialDataIntoTable(infile); // close the file after we are done using it infile.close(); // get the number of threads from the command line numSearchThreads = atoi(argv[2]); // initialize the search thread array with the number // specified from the commandline searchRecordThreads = new pthread_t[numSearchThreads]; // initialize the new records thread array with the // specified number getNewRecordThreads = new pthread_t[NUM_NEW_RECORDS_THREADS]; // get a key for our msg queue key = ftok("/bin/ls", 'O'); // check if we got a valid key if(key < 0) { perror("ftok error"); exit(1); } // get a msg ID msqid = msgget(key, MSG_Q_ID | IPC_CREAT); // check if we got a valid ID if(msqid < 0) { perror("msgget error"); exit(1); } cout<<"n** SERVER ID #"<<msqid<<" SUCCESSFULLY ESTABLISHEDn"<<endl; // infinite loop to send/recieve messages to/from client do{ // recieve record from client if(msgrcv(msqid, &msg, sizeof(msg) - sizeof(long), CLIENT_TO_SERVER_CHANNEL, 0) < 0) { perror("msgsnd error"); exit(1); } // save the recieved record from the client into a linked list // this is used in the "SearchRecords" function recievedMsg.push_back(msg.recordID); // --- SEARCH RECORDS THREADS // keep track of how many threads are being used if(searchThreadNum > numSearchThreads-1) { searchThreadNum = 0; } // create threads & send them to work if(pthread_create(&searchRecordThreads[searchThreadNum], NULL, &SearchRecords, NULL) < 0) { perror("pthread_create error"); exit(1); } // wait for threads to finish pthread_join(searchRecordThreads[searchThreadNum], NULL); // --- GENERATE NEW RECORDS THREADS // keep track of how many threads are being used if(newRecThreadNum > NUM_NEW_RECORDS_THREADS-1) { newRecThreadNum = 0; } // create threads & send them to work if(pthread_create(&getNewRecordThreads[newRecThreadNum], NULL, &GenerateNewRecord, NULL) < 0) { perror("pthread_create error"); exit(1); } // wait for threads to finish pthread_join(getNewRecordThreads[newRecThreadNum], NULL); // --- INCREMENT NUMBER OF THREADS BEING USED //cout<<searchThreadNum<<endl; ++searchThreadNum; ++newRecThreadNum; }while(true); return 0; }// end of main void* GenerateNewRecord(void* args) { const char* 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"}; Record temp; int record = rand()%10000; int nameLen = sizeof(names)/sizeof(names[0]); // lock the current hash table cell if(pthread_mutex_lock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0) { perror("pthread_mutex_lock error"); exit(1); } // put the new data into the hash table temp.id = record; strncpy(temp.firstName, names[rand()%(nameLen-1)], sizeof(temp.firstName)); strncpy(temp.lastName, names[rand()%(nameLen-1)], sizeof(temp.lastName)); hashTable[record%HASH_TABLE_SIZE].cell.push_back(temp); pthread_mutex_init(&hashTable[temp.id%HASH_TABLE_SIZE].mutex, NULL); // unlock the current hash table cell if(pthread_mutex_unlock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0) { perror("pthread_mutex_lock error"); exit(1); } return 0; }// end of GenerateNewRecord void* SearchRecords(void* args) { int record = 0; bool found = false; // get the record from the client to search the hash table if(!recievedMsg.empty()) { record = recievedMsg.front(); recievedMsg.pop_front(); } //cout<<endl<<record<<endl; // if the current hash table cell isnt empty, search for the record id if(!hashTable[record%HASH_TABLE_SIZE].cell.empty()) { // lock the current hash table cell if(pthread_mutex_lock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0) { perror("pthread_mutex_lock error"); exit(1); } // search hash table cell to see if given record is there for(list<Record>::iterator iter = hashTable[record%HASH_TABLE_SIZE].cell.begin(); iter != hashTable[record%HASH_TABLE_SIZE].cell.end(); ++iter) { // we found a match in the hash table if(iter->id == record) { // set the data fields of the found record // to prepare it to be sent over the message queue SendRecord(iter->id, iter->firstName, iter->lastName); found = true; break; } } // unlock the current hash table cell if(pthread_mutex_unlock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0) { perror("pthread_mutex_lock error"); exit(1); } } // if we didnt find a record, tell that to the client if(!found) { SendRecord(-1, "Record Not Found!", ""); } return 0; }// end of SearchRecords void SendRecord(int id, const char* firstName, const char* lastName) { MsgQueue msg; // instantiate a message queue // set the message queue channel msg.messageType = SERVER_TO_CLIENT_CHANNEL; // set the record id msg.recordID = id; // set the record name strncpy(msg.recordName, firstName, sizeof(msg.recordName)); strncat(msg.recordName, " ", sizeof(msg.recordName)); strncat(msg.recordName, lastName, sizeof(msg.recordName)); // send record to client if(msgsnd(msqid, &msg, sizeof(msg) - sizeof(long), 0) < 0) { perror("msgsnd error"); exit(1); } }// end of SendRecord void InsertInitialDataIntoTable(ifstream& infile) { Record temp; while(infile>>temp.id >>temp.firstName >>temp.lastName) { hashTable[temp.id%HASH_TABLE_SIZE].cell.push_back(temp); pthread_mutex_init(&hashTable[temp.id%HASH_TABLE_SIZE].mutex, NULL); } }// end of InsertInitialDataIntoTable void SignalHandler(int arg) { cerr<<"nnCaught the CTRL-Cn" <<"Shutting down the server connection..n"; // deallocate the queue if(msgctl(msqid, IPC_RMID, NULL) < 0) { perror("msgctl error"); } exit(0); }// http://programmingnotes.org/ |
The client program has a much easier flow of control. It is implemented below.
==== 4. CLIENT ====
The client has the following structure and function:
The client program was designed to sleep for 1 second every time a new record is obtained from the server. This makes it so its easier for the user to see what is being displayed on the screen.
The client program is invoked with the following commandline structure:
./client
The client is implemented below.
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// ============================================================================= // Author: K Perkins // Date: Oct 5, 2013 // Taken From: http://programmingnotes.org/ // File: Client.cpp // Description: Using a Hash Table, this program simulates a server and client // application. The server program maintains a hash table of records and // a pool of threads. The client requests records from the server by sending // record ID's over the message queue. The server retrieves a request from // the message queue and wakes up a thread in the thread pool. The awakened // thread then uses the ID to retrieve the corresponding record from the // hash table and sends the record to the client over the message queue. // // This is the client program which connects to the message queue that the // server previously establishes using the msgget() system call. It checks // the message queue for sucessfully found records using the msgrcv() system // call, and uses the msgsnd system call to send new search records back to // the server, where it searches for new records // // NOTE: This file is set to display records on a 1 second delay // ============================================================================= #include <iostream> #include <cstdlib> #include <ctime> #include <unistd.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> using namespace std; // Compile & Run // g++ Client.cpp -o Client // ./Client // message queue structure struct MsgQueue { // the channel the connection will be on long messageType; int recordID; char recordName[100]; }; // constant variables const int HOW_LONG_TO_SLEEP = 1; const int CLIENT_TO_SERVER_CHANNEL = 2; const int SERVER_TO_CLIENT_CHANNEL = 4; const int MSG_Q_ID = 0664; int main() { // declare variables MsgQueue msg; srand(time(NULL)); key_t key = 0; int msqid = 0; // message queue ID // get a key for the queue key = ftok("/bin/ls", 'O'); // check if we got a valid key if(key < 0) { cerr<<"ftok"; exit(1); } // get the ID of the queue msqid = msgget(key,MSG_Q_ID); // check if we got a valid ID if(msqid < 0) { cerr<<"n** ERROR - CONNECTION TO SERVER NOT FOUNDnn"; exit(1); } cerr<<"n** CONNECTION TO SERVER ID #"<<msqid<<" SUCCESSn"<<endl; // infinite loop to send/recieve messages from server do{ // connect to the server msg.messageType = CLIENT_TO_SERVER_CHANNEL; // generate a random search key msg.recordID = rand()%10000; // send record search to the server if(msgsnd(msqid, &msg, sizeof(msg) - sizeof(long), 0) < 0) { cerr<<"n** SERVER CONNECTION CLOSED..nn"; exit(1); } // recieve a record from the server if(msgrcv(msqid, &msg, sizeof(msg) - sizeof(long), SERVER_TO_CLIENT_CHANNEL, 0) < 0) { cerr<<"n** SERVER CONNECTION CLOSED..nn"; exit(1); } // if we found a valid record, display it to the screen if(msg.recordID > 0) { cerr<< "ID = "<<msg.recordID<<" tRecord = "<<msg.recordName<<endl; sleep(HOW_LONG_TO_SLEEP); } }while(true); return 0; }// http://programmingnotes.org/ |
QUICK NOTES:
The highlighted lines are sections of interest to look out for.
The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.
See sample files named server.cpp and client.cpp which illustrate interprocess communications using message queues. See file condvar.cpp which illustrates the use of condition variables. Finally, see file signal.cpp which illustrates the overriding of default signal handlers.
The following is sample output:
(Note: remember to include the initial records input file!)
SERVER OUTPUT:
./Server INPUT_Records_programmingnotes_freeweq_com.txt 26** SERVER ID #1015808 SUCCESSFULLY ESTABLISHED
^C
Caught the CTRL-C
Shutting down the server connection..
CLIENT OUTPUT:
./Client** CONNECTION TO SERVER ID #1015808 SUCCESS
ID = 243 Record = Graham Basil
ID = 7943 Record = Tobias Arie
ID = 3607 Record = Claire Amina
ID = 849 Record = Jetta Victoria
ID = 126 Record = Jeramy Tod
ID = 7483 Record = Vivan Krystal
ID = 8036 Record = Lilliam Harley
ID = 1901 Record = Kati Basil
ID = 3524 Record = Kenneth Perkins
ID = 5256 Record = Jodee Albertina
ID = 7065 Record = Marylou Donn
ID = 3951 Record = Ula Domitila
ID = 395 Record = Jaime Lilliam
ID = 9234 Record = Nigel Gene
ID = 4148 Record = Carmella Evelia
ID = 9340 Record = Sang Cherilyn
ID = 3834 Record = Jessica Freddy** SERVER CONNECTION CLOSED..
C++ || Custom Template Hash Map With Iterator Using Separate Chaining
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 ===
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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.
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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-> 462These are all of the items in the entire hash map:
Key-> CIS Value-> 465Key-> DANCE Value-> 134
Key-> PE Value-> 145
Key-> PE Value-> 125Key-> MATH Value-> 270
Key-> MATH Value-> 150Key-> GEOL Value-> 201
Key-> GEOL Value-> 101Key-> CPSC Value-> 120
Key-> CPSC Value-> 131
Key-> CPSC Value-> 240
Key-> CPSC Value-> 301
Key-> CPSC Value-> 462Key-> BIOL Value-> 585
Key-> BIOL Value-> 134Key-> ART Value-> 101
Key-> ART Value-> 345Key-> CHEM Value-> 185
Key-> HIST Value-> 251
The total number of items in the hash map is: 19
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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 carsThese are all of the cars in the hash map:
Jessica's car(s)
Car: Nissan Altima
Year: 2011
MPG: 30.7Kenneth's car(s)
Car: Ford Fusion
Year: 2006
MPG: 28.5Car: BMW 535i
Year: 2014
MPG: 25.4Car: 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: 30.7Kenneth's car(s)
Car: Acura Integra
Year: 2001
MPG: 20.2Car: BMW 535i
Year: 2014
MPG: 25.4Car: 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: 30.7Kenneth's car(s)
Car: BMW 535i
Year: 2014
MPG: 25.4Car: Ford Fusion
Year: 2006
MPG: 28.5
-----------------------------------------------------The total number of cars in the hash map is: 3
C++ || Simple Spell Checker Using A Hash Table
The following is another programming assignment which was presented in a C++ Data Structures course. This assignment was used to gain more experience using hash tables.
REQUIRED KNOWLEDGE FOR THIS PROGRAM
Hash Table - What Is It?
How To Create A Spell Checker
How To Read Data From A File
Strtok - Split Strings Into Tokens
#include 'HashTable.h'
The Dictionary File - Download Here
== OVERVIEW ==
This program first reads words from a dictionary file, and inserts them into a hash table.
The dictionary file consists of a list of 62,454 correctly spelled lowercase words, separated by whitespace. The words are inserted into the hash table, with each bucket growing dynamically as necessary to hold all of the incoming data.
After the reading of the dictionary file is complete, the program prompts the user for input. After input is obtained, each word that the user enteres into the program is looked up within the hash table to see if it exists. If the user entered word exists within the hash table, then that word is spelled correctly. If not, a list of possible suggested spelling corrections is displayed to the screen.
== HASH TABLE STATISTICS ==
To better understand how hash tables work, this program reports the following statistics to the screen:
• The total size of the hash table.
• The size of the largest hash table bucket.
• The size of the smallest hash table bucket.
• The total number of buckets used.
• The average hash table bucket size.
A timer is used in this program to time (in seconds) how long it takes to read in the dictionary file. The program also saves each hash table bucket into a separate output .txt file. This is used to further visualize how the hash table data is internally being stored within memory.
== SPELL CHECKING ==
The easiest way to generate corrections for a spell checker is via a trial and error method. If we assume that the misspelled word contains only a single error, we can try all possible corrections and look each up in the dictionary.
Example:
wird: bird gird ward word wild wind wire wiry
Traditionally, spell checkers look for four possible errors: a wrong letter (“wird”), also knows as alteration. An inserted letter (“woprd”), a deleted letter (“wrd”), or a pair of adjacent transposed letters (“wrod”).
The easiest of which is checking for a wrong letter. For example, if a word isnt found in the dictionary, all variants of that word can be looked up by changing one letter. Given the user input “wird,” a one letter variant can be “aird”, “bird”, “cird”, etc. through “zird.” Then “ward”, “wbrd”, “wcrd” through “wzrd”, can be checked, and so forth. Whenever a match is found within the dictionary, the spelling correction should be displayed to the screen.
For a detailed analysis how the other methods can be constructed, click here.
===== SIMPLE SPELL CHECKER =====
This program uses a custom template.h class. To obtain the code for that class, click here.
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// ============================================================================ // Author: Kenneth Perkins // Date: Jan 31, 2013 // Taken From: http://programmingnotes.org/ // File: SpellCheck.cpp // Description: This is a simple spell checker which tests the HashTable.h // class. // ============================================================================ #include <iostream> #include <fstream> #include <cctype> #include <cstring> #include <string> #include <iomanip> #include <ctime> #include <limits> #include "HashTable.h" using namespace std; // iterator declaration for hash table typedef HashTable<string>::Iterator iterDec; // hash table size const int TABLE_SIZE = 19000; // strtok delimiters const char* DELIMITERS = " ,.-\':;?()+*/\\%$#!\"@\^&"; // function prototypes void PrintTableStats(HashTable<string>& hashTable); int SpellCheck(HashTable<string>& hashTable, string word); string ToLowerCase(string word); int main() { // declare variables int result = 0; string userInput; string currWord; clock_t beg; // used to time the hashtable load clock_t end; // used to time the hashtable load char response; ifstream infile; HashTable<string> hashTable(TABLE_SIZE); // open the dictionary file infile.open("INPUT_Dictionary_programmingnotes_freeweq_com.txt"); // check if the file exists, EXIT if it doesnt if(infile.fail()) { cout<<"\n\n**ERROR - The dictionary file could not be found...\n"; exit(1); } cerr<<"\nLoading dictionary...."; beg = clock(); // start the timer // get data from file and put into hashtable while(infile >> currWord) { // makes sure duplicate words arent inserted into table if(!hashTable.Count(currWord)) { hashTable.Insert(currWord); } } infile.close(); PrintTableStats(hashTable); end = clock()-beg; // end the timer cout<<"\n\nDictionary loaded in "<< (double)end / ((double)CLOCKS_PER_SEC)<<" secs!"; // creates a line separator cout<<endl; cout.fill('-'); cout<<left<<setw(50)<<""<<endl; do{ // get user input cout<<"\n>> Please enter a sentence: "; getline(cin,userInput); cout<<endl; // split each word from the string into individual words to check if // they are spelled correctly char* splitInput = strtok(const_cast<char*>(userInput.c_str()),DELIMITERS); while(splitInput!=NULL) { currWord = splitInput; currWord = ToLowerCase(currWord); result += SpellCheck(hashTable,currWord); splitInput = strtok(NULL,DELIMITERS); } // display results if(result > 0) { cout<<"Number of words spelled incorrectly: "<<result<<endl; result = 0; } // ask for more data cout<<"\nDo you want to enter another sentence? (y/n): "; cin >> response; cin.ignore(numeric_limits<streamsize>::max(),'\n'); // clear the cin buffer }while(toupper(response)=='Y'); cout<<"\nBYE!!\n"; return 0; }// end of main void PrintTableStats(HashTable<string>& hashTable) { int largestBucket = -9999999; int largestIndex = 0; int smallestBucket = 9999999; int smallestIndex = 0; double numBuckestUsed = 0; ofstream outfile("OUTPUT_HashTable_Stats_programmingnotes_freeweq_com.txt"); for(int x=0; x < hashTable.TableSize(); ++x) { // iterator is used to traverse each hashtable bucket iterDec it = hashTable.begin(x); if(!hashTable.IsEmpty(x)) { if(smallestBucket > hashTable.BucketSize(x)) { smallestBucket = hashTable.BucketSize(x); smallestIndex = x; } if(largestBucket < hashTable.BucketSize(x)) { largestBucket = hashTable.BucketSize(x); largestIndex = x; } ++numBuckestUsed; outfile<<"\nBucket #"<<x<<":\n"; for(int y = 0; y < hashTable.BucketSize(x); ++y) { outfile <<"\t"<< it[y] << endl; } } } cout<<"Complete!\n"; // creates a line separator cout<<endl; cout.fill('-'); cout<<left<<setw(50)<<""<<endl; cout<<"Total dictionary words = "<<hashTable.TotalElems()<<endl <<"Hash table size = "<<hashTable.TableSize()<<endl <<"Largest bucket size = "<<largestBucket<< " items at index #"<<largestIndex<<endl <<"Smallest bucket size = "<<smallestBucket<< " items at index #"<<smallestIndex<<endl <<"Total buckets used = "<<numBuckestUsed<<endl <<"Total percent of hash table used = "<<(numBuckestUsed/hashTable.TableSize())*100<<"%"<<endl <<"Average bucket size = "<<(hashTable.TotalElems()/numBuckestUsed)<<" items"; }// end of PrintTableStats int SpellCheck(HashTable<string>& hashTable, string word) { int result = 0; int suggestion = 0; string remove[256]; int numRemove=0; if(!hashTable.Count(word)) { ++result; cout<<"** "<<word<<": "; // alteration & insertion for(unsigned x = 0; x < word.length(); ++x) { string alteration = word; for(char c = 'a'; c <= 'z'; ++c) { //alteration alteration[x] = c; if(hashTable.Count(alteration)) { cout<<alteration<<", "; remove[numRemove++] = alteration; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(alteration); } //insertion string insertion = word.substr(0, x) + c + word.substr(x); if(hashTable.Count(insertion)) { cout<<insertion<<", "; remove[numRemove++] = insertion; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(insertion); } } } // transposition & deletion for(unsigned x = 0; x < word.length()-1;++x) { // transposition string transposition = word.substr(0,x) + word[x+1] + word[x] + word.substr(x+2); if(hashTable.Count(transposition)) { cout<<transposition<<", "; remove[numRemove++] = transposition; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(transposition); } // deletion string deletion = word.substr(0, x)+ word.substr(x + 1); if(hashTable.Count(deletion)) { cout<<deletion<<", "; remove[numRemove++] = deletion; ++suggestion; // remove the entry so it isnt displayed multiple times hashTable.Remove(deletion); } } // place the removed items back inside the hash table while(numRemove>=0) { hashTable.Insert(remove[numRemove--]); } if(suggestion < 1) { cout<<"No spelling suggestion found..."; } cout<<endl<<endl; } return result; }// end of SpellCheck string ToLowerCase(string word) { for(unsigned x = 0; x < word.length(); ++x) { word[x] = tolower(word[x]); } return word; }// http://programmingnotes.org/ |
QUICK NOTES:
The highlighted lines are sections of interest to look out for.
The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.
Remember to include the data file.
Once compiled, you should get this as your output
Loading dictionary....Complete!--------------------------------------------------
Total dictionary words = 61286
Hash table size = 19000
Largest bucket size = 13 items at index #1551
Smallest bucket size = 1 items at index #11
Total buckets used = 18217
Total percent of hash table used = 95.8789%
Average bucket size = 3.36422 itemsDictionary loaded in 1.861 secs!
-------------------------------------------------->> Please enter a sentence: wird
** wird: bird, gird, ward, weird, word, wild, wind, wire, wired, wiry,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: woprd
** woprd: word,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: wrd
** wrd: ard, ord, ward, wed, word,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: wrod
** wrod: brod, trod, wood, rod, word,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: New! Safe and efective
** efective: defective, effective, elective,
Number of words spelled incorrectly: 1
Do you want to enter another sentence? (y/n): y
--------------------------------------------------
>> Please enter a sentence: This is a sentance with no corections gygyuigigigiug
** sentance: sentence,
** corections: corrections,
** gygyuigigigiug: No spelling suggestion found...
Number of words spelled incorrectly: 3
Do you want to enter another sentence? (y/n): n
BYE!!
C++ || Custom Template Hash Table With Iterator Using Separate Chaining
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 ===
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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.
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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 HomerNow bucket #0 has 9 items
The first element in bucket #0 is TamraThe unsorted items in strHash bucket #0:
it[] = Tamra
it[] = Lyndon
it[] = Johanna
it[] = Perkins
it[] = Alva
it[] = Jordon
it[] = Neville
it[] = Lawrence
it[] = JettaThe sorted items in strHash bucket #0:
it[] = Alva
it[] = Jetta
it[] = Johanna
it[] = Jordon
it[] = Lawrence
it[] = Lyndon
it[] = Neville
it[] = Perkins
it[] = Tamra
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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 = RogerstrHash Bucket #1:
*it = Lilliam
*it = Lilliam
*it = ThedastrHash Bucket #2:
*it = AriestrHash Bucket #3:
*it = MagdastrHash Bucket #6:
*it = Edda
*it = Irvin
*it = Kati
*it = LyndonstrHash Bucket #7:
*it = Deb
*it = JaimestrHash Bucket #8:
*it = Neville
*it = VictoriastrHash Bucket #9:
*it = Chery
*it = Evelia--------------------------------------------
intHash Bucket #0:
it[] = 2449
it[] = 6135intHash Bucket #1:
it[] = 1120
it[] = 852intHash Bucket #2:
it[] = 5727intHash Bucket #3:
it[] = 1174intHash Bucket #4:
it[] = 2775
it[] = 3525
it[] = 8375intHash Bucket #5:
it[] = 4322
it[] = 8722
it[] = 5016intHash Bucket #6:
it[] = 5053
it[] = 7231
it[] = 1571intHash Bucket #7:
it[] = 1666
it[] = 4510
it[] = 1548
it[] = 3646intHash Bucket #9:
it[] = 2756--------------------------------------------
strctHash Bucket #0:
it-> = Cherilyn
it-> = RogerstrctHash Bucket #1:
it-> = Tamra
it-> = Alex
it-> = ThedastrctHash Bucket #2:
it-> = Nigel
it-> = Alva
it-> = AriestrctHash Bucket #4:
it-> = BasilstrctHash Bucket #5:
it-> = TodstrctHash Bucket #6:
it-> = Irvin
it-> = LyndonstrctHash Bucket #7:
it-> = Amina
it-> = Hillary
it-> = Kenneth
it-> = AminastrctHash Bucket #8:
it-> = Gene
it-> = Lemuel
it-> = GenestrctHash Bucket #9:
it-> = Albertina
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