Week 14: Assignment - Hash Collisions
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cmake_minimum_required(VERSION 3.16)
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project(week-14)
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set(CMAKE_CXX_STANDARD 14)
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add_executable(week-14 main.cpp)
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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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* Champlain College SDEV-345-81
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*
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* C++ Week 14 Quadratic Probing, Hash Tables - (2020/12/13)
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*
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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*
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* Modify last week's program to demonstrate quadratic hash probing when a collision occurs.
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*
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* LAST WEEK
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* Write a menu driven program that creates a hash table using an array.
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* The program should give the user the following options and should run in an infinite loop:
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* 1) Insert key
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* 2) Delete key
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* 3) Display hash table
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* 4) Find key
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* The key should be a string and the program should calculate the location using a hash function.
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* The program should also prompt the user when there is a collision and when the hash table is full.
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*
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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*
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* Written by Llewellyn van der Merwe <llewellyn.vandermerw@mymail.champlain.edu>, December 2020
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* Copyright (C) 2020. All Rights Reserved
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* License GNU/GPL Version 2 or later - http://www.gnu.org/licenses/gpl-2.0.html
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*
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
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#include <iostream>
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#include <string>
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#include <limits>
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using namespace std;
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class HashTable {
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private:
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// never use this as a value ;)
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const string emptyString = "|//_-++-_0.^.0_-++-_\\|";
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// the size of the array
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static const int tableSize = 8;
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// the inserted number
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int inserted = 0;
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// the HashBucket table array of nodes
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string HashBucket[tableSize];
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// found & empty key
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static const int emptyFoundKey = tableSize + 10;
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// found ;)
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int foundKey = emptyFoundKey;
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// empty ;)
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int emptyKey = emptyFoundKey;
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// search for value in table
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bool find(string &value) {
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// get the HashBucket value of the string
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int key = Hash(value);
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// check if the value is found
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if (HashBucket[key] == value) {
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// if found set key
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foundKey = key;
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// found
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return true;
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}
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// continue the search
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return find(key, value);
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}
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// smart search by key and value
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bool find(int &key, string &value) {
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// always reset the found
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emptyKey = emptyFoundKey;
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foundKey = emptyFoundKey;
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// use quadratic probing
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for (int pos = 0; pos < tableSize; pos++) {
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// Computing the new hash value
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key = Quadratic(key, pos);
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// check if the value is found
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if (HashBucket[key] == value) {
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// if found set key
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foundKey = key;
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// we found the value
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return true;
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} else if (HashBucket[key] == emptyString && emptyKey == emptyFoundKey) {
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// if first not found set key
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emptyKey = key;
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// but lets continue the search since on removal
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// we do not move the values to spaces
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// up to fill the array from the first hash
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}
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}
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return false;
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}
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// Hash function
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int Hash(string key) {
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int hash = 0;
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int tmp = key.length();
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// now loop the string value-key to get HashBucket
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for (int i = 0; i < tmp; i++) {
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hash = hash + (int) key[i];
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}
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// return the remainder
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return hash % tableSize;
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}
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// quadratic insert function
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bool insert(int &key, string &value) {
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// check if key was found
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if (key != emptyFoundKey && HashBucket[key] == emptyString) {
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// since we have the key
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// we need to do the search
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// again
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HashBucket[key] = value;
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// count values inserted
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inserted++;
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// always reset just incase
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emptyKey = emptyFoundKey;
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return true;
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}
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// get the HashBucket value of the string
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key = Hash(value);
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// use quadratic probing
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for (int pos = 0; pos < tableSize; pos++) {
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// Computing the new hash value
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key = Quadratic(key, pos);
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if (HashBucket[key] == emptyString) {
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// Break the loop after
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// inserting the value
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// in the table
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HashBucket[key] = value;
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// count values inserted
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inserted++;
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return true;
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}
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}
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return false;
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}
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// quadratic function
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int Quadratic(int key, int pos) {
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// Computing the new hash value
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int hash = key + pos * pos;
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// return the remainder
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return hash % tableSize;
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}
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public:
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// our constructor of our HashBucket table
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HashTable() {
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// initialize the empty HashBucket tables
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for (int i = 0; i < tableSize; i++) {
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HashBucket[i] = emptyString;
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}
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}
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// check if table is full
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bool isFull() {
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return inserted == tableSize;
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}
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// add a node value
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void insert(string value) {
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// get the HashBucket value of the string
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int key = Hash(value);
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// check if the HashBucket has a collision
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if (HashBucket[key] == emptyString) {
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// give success adding info
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cout << "█ [Info] " << value << " - added successfully." << endl;
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// new value
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HashBucket[key] = value;
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// count values inserted
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inserted++;
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}
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// check if the value exist
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else if (!find(value)) {
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// prom the user if we should add to table
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cout << "█ [Warning] Collision detected." << endl;
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cout << "█ Do you still want to add: " << value << endl;
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cout << "█ Enter initial [yes/no]: ";
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char choice;
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cin >> choice;
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if ((choice == 'y' || choice == 'Y') && insert(emptyKey, value)) {
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// give collision info
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cout << "██████████████████████████████████████████████████████████" << endl;
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cout << "█ Collision resolved!" << endl;
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cout << "█ [Info] " << value << " - quadratic probing used." << endl;
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} else if (choice == 'y' || choice == 'Y') {
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// give error of quadratic probing failure
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cout << "██████████████████████████████████████████████████████████" << endl;
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cout << "█ [Error] " << value << " - not added." << endl;
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cout << "█ [Error] " << " - Quadratic probing failed." << endl;
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cout << "█ [Error] " << " - The array needs to be enlarged." << endl;
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} else {
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// give notice
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cout << "█ [Notice] " << value << " - not added." << endl;
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}
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} else {
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// give exists error
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cout << "█ [Error] " << value << " - exists." << endl;
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}
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cout << "██████████████████████████████████████████████████████████" << endl;
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return;
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}
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// search if the value is in the hash table
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void search(string &value) {
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// use the find method/function
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if (find(value)) {
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cout << "█ [Success] (" << foundKey << ") => " << value << " - found" << endl;
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} else {
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cout << "█ [Notice] " << value << " - not found" << endl;
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}
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cout << "██████████████████████████████████████████████████████████" << endl;
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return;
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}
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// display the hash table
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void display() {
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cout << "███ THE HASH TABLE ███████████████████████████████████████" << endl;
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cout << "██████████████████████████████████████████████████████████" << endl;
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for (int i = 0; i < tableSize; i++) {
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// only print out if bucket has values
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if (HashBucket[i] != emptyString) {
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cout << "█ (" << i << ") => ";
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cout << HashBucket[i] << endl;
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cout << "██████████████████████████████████████████████████████████" << endl;
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} else {
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// empty notice
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cout << "█ (" << i << ") =-" << endl;
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cout << "██████████████████████████████████████████████████████████" << endl;
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}
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}
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if (isFull()) {
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cout << "███ TABLE IS FULL ████████████████████████████████████████" << endl;
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} else {
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cout << "███ TABLE NOT FULL ███████████████████████████████████████" << endl;
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}
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return;
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}
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// delete a value from the table
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void remove(string value) {
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// value found so remove
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if (find(value)) {
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// move the next node up
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HashBucket[foundKey] = emptyString;
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// count value removed
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inserted--;
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// removed notice
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cout << "█ [Success] " << value << " - removed." << endl;
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} else {
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// not found notice
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cout << "█ [Notice] " << value << " - not found." << endl;
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}
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cout << "██████████████████████████████████████████████████████████" << endl;
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return;
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}
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};
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int main() {
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// instantiate the table
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HashTable Table;
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// program loop (taken and adapted from this weeks module)
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char choice = 'b';
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string aKey;
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// start the program
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cout << "██████████████████████████████████████████████████████████" << endl;
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// interact with user
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while (choice != 'x') {
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// check if the table is full
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if (Table.isFull()) {
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cout << "█ Enter first letter of "
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<< "show, delete, or find: ";
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} else {
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cout << "█ Enter first letter of "
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<< "show, insert, delete, or find: ";
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}
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char choice;
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cin >> choice;
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// clear cin stream
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cin.clear();
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cin.ignore(numeric_limits<streamsize>::max(), '\n');
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switch (choice) {
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case 's':
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Table.display();
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break;
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case 'i':
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if (Table.isFull()) {
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cout << "█ Table is full" << endl;
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} else {
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cout << "█ Enter key value to insert: ";
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getline(cin, aKey);
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// now insert the string
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Table.insert(aKey);
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}
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break;
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case 'd':
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cout << "█ Enter key value to delete: ";
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getline(cin, aKey);
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// now remove the string
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Table.remove(aKey);
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break;
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case 'f':
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cout << "█ Enter key value to find: ";
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getline(cin, aKey);
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// now search for the string
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Table.search(aKey);
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break;
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default:
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cout << "█ Invalid entry" << endl;
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break;
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}
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}
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}
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