added Hash Table #160

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Expand Up		@@ -26,6 +26,15 @@ This repo contains the following sections implemented in JavaScript

		Find the detailed contents and problem list here: [Table Of Contents](TOC.md)

	## Contributors

	\| Name \| Twitter \| LinkedIn \| Website \|
	\| ----------------------------------------- \| ------------------------------------------- \| --------------------------------------------- \| ------------------------------------------ \|
	\| [Ashok Dey](https://github.com/ashokdey) \| [ashokdey\_](https://twitter.com/ashokdey_) \| [Ashok Dey](https://linkedin.com/in/ashokdey) \| [https://ashokdey.in](https://ashokdey.in) \|
	\| [Ashu Deshwal](https://github.com/TheSTL) \| [\_TheSTL\_](https://twitter.com/_TheSTL_) \| - \| - \|

	[Detailed list of contributors](https://github.com/knaxus/problem-solving-javascript/graphs/contributors)

		## Contribution Guide

		It's great to know that you want to contribute to this repo. Thanks for taking interest. please fing the [guide here](https://github.com/knaxus/problem-solving-javascript/blob/master/CONTRIBUTING.md)
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1 change: 1 addition & 0 deletions TOC.md

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Expand Up		@@ -49,6 +49,7 @@
		- Problems
		- [K Largest Elements](src/_DataStructures_/Heaps/k-largest-in-array)
		- [K Smallest Elements](src/_DataStructures_/Heaps/k-smallest-in-array)
	- [Hash Table](src/_DataStructures_/HashTable)

		### Logical Problems

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9 changes: 9 additions & 0 deletions src/_DataStructures_/HashTable/HashEntry.js

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		@@ -0,0 +1,9 @@
	class HashEntry {
	constructor({ key, value }) {
	this.key = key;
	this.value = value;
	this.next = null;
	}
	}

	module.exports = HashEntry;

225 changes: 225 additions & 0 deletions src/_DataStructures_/HashTable/index.js

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		@@ -0,0 +1,225 @@
	const HashEntry = require('./HashEntry');

	class HashTable {
	constructor(slots, { allowResize = true, strongHash = true, custonHash = null }) {
	// init with a default set of slots
	this.slot = slots \|\| 19;
	// size to hold the current size
	// and help to resize when the table is half filled
	this.size = 0;
	// threshold (let it be 70%)
	this.threshold = 0.7;
	// the main bucket
	this.bucket = new Array(this.slot);
	this.allowResize = allowResize;
	this.strongHash = strongHash;
	if (custonHash) {
	// eslint-disable-next-line no-underscore-dangle
	this._hash = custonHash;
	}

	// fill the bucket with null
	for (let i = 0; i < this.slot; i += 1) this.bucket[i] = null;
	}

	_hash(key) {
	// convert the key to String;
	const stringKey = String(key);

	let index = 0;
	const PRIME_MULTIPLIER = 1801; // Random prime number
	const PRIME_ADDER = 2029; // Random prime number

	// loop till the length of the key or max 100
	const loopTill = Math.min(stringKey.length, 100);

	for (let i = 0; i < loopTill; i += 1) {
	const char = stringKey[i];
	const value = char.charCodeAt(0) - 96;
	index = (index * PRIME_MULTIPLIER + value) % this.bucket.length;
	if (this.strongHash) {
	index = (index + PRIME_ADDER) % this.bucket.length;
	}
	}
	return index;
	}

	_resize() {
	const oldSlot = this.slot;
	const oldBucket = this.bucket;

	this.slot = oldSlot * 2;
	const newBucket = new Array(this.slot);
	// fill the new bucket with nulls
	for (let i = 0; i < this.slot; i += 1) newBucket[i] = null;

	this.bucket = newBucket;

	for (let i = 0; i < oldSlot; i += 1) {
	if (oldBucket[i]) {
	let head = oldBucket[i];

	while (head !== null) {
	const { key, value } = head;
	// eslint-disable-next-line no-underscore-dangle
	const newIndex = this._hash(key);
	// eslint-disable-next-line no-underscore-dangle
	this._push(newIndex, { key, value });
	head = head.next;
	}
	}
	}
	}

	_push(index, value) {
	/**
	* Utility to add a SLL to the index in case of more than one
	* key hashes to the same index
	*/
	const node = new HashEntry(value);
	if (!this.bucket[index]) {
	this.bucket[index] = node;
	this.size += 1;
	return index;
	}

	let head = this.bucket[index];
	// extract the key and see if it already exists
	const { key, value: newValue } = value;

	// traverse to the end
	while (head.next !== null) {
	if (head.key === key) {
	// overridet the value with the new value
	head.value = newValue;
	return index;
	}
	head = head.next;
	}
	// if the key was not found
	head.next = node;
	this.size += 1;
	return index;
	}

	_value(index, key) {
	let head = this.bucket[index];
	while (head !== null) {
	if (head.key === key) {
	return head.value;
	}
	head = head.next;
	}
	return null;
	}

	// eslint-disable-next-line class-methods-use-this
	_convertNodesToSLL(nodeCollection) {
	// convert collection of nodes into a SLL
	let head = nodeCollection[0];
	const start = head;
	let i = 1;
	while (i < nodeCollection.length) {
	head.next = nodeCollection[i];
	i += 1;
	head = head.next;
	}

	return start;
	}

	set(key, value) {
	// eslint-disable-next-line no-underscore-dangle
	const index = this._hash(key);
	// storing value as an key-value pair
	// eslint-disable-next-line no-underscore-dangle
	this._push(index, { key, value });

	/**
	* calculate the load factor, if it's greater than threshold
	* resize the hash table
	*/
	const loadFactor = Number((this.size / this.slot).toFixed(1));
	if (loadFactor > this.threshold && this.allowResize) {
	// console.log('Resizing hash table');
	// eslint-disable-next-line no-underscore-dangle
	this._resize();
	}
	}

	get(key) {
	// get the index for the given key
	// eslint-disable-next-line no-underscore-dangle
	const index = this._hash(key);
	if (!this.bucket[index]) return null;
	// eslint-disable-next-line no-underscore-dangle
	return this._value(index, key);
	}

	remove(key) {
	// get the index
	// eslint-disable-next-line no-underscore-dangle
	const index = this._hash(key);

	// get the SLL using the index
	let head = this.bucket[index];
	// return null if the head is null
	if (!head) {
	return null;
	}

	if (head.key === key) {
	let node = head;
	this.bucket[index] = head.next;
	const val = { key, value: node.value };
	node = null;
	this.size -= 1;
	return val;
	}

	let previous = null;

	while (head !== null) {
	if (head.key === key) {
	let node = head;
	previous.next = head.next;
	this.size -= 1;
	const res = { key, value: node.value };
	node = null;
	return res;
	}
	previous = head;
	head = head.next;
	}
	return null;
	}

	getSize() {
	return this.size;
	}

	isEmpty() {
	return this.size === 0;
	}
	}

	// const ht = new HashTable(5, { allowResize: false, strongHash: false });
	// ht.set('maroon', 'I maroon');
	// ht.set('hello', 'I am a new value');
	// console.log(ht.bucket);
	// ht.set('hell', 'Bad value');
	// ht.set('hello', 'I am a yet another value');
	// ht.set('yellow', 'I am yellow');

	// console.log(ht.get('hello'));
	// console.log(ht.get('maroon'));
	// console.log(ht.bucket);

	// console.log('deleting hello........');
	// console.log(ht.remove('hello'));
	// console.log(ht.bucket);

	// console.log(ht.remove('yellow'));
	// console.log(ht.bucket);

	module.exports = HashTable;

4 changes: 2 additions & 2 deletions src/_DataStructures_/LinkedList/index.js

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		@@ -1,8 +1,8 @@
	// do not change the node class, you never know how many things it caan break! :)
	// do not change the node class, you never know how many things it caan break! :)
		class Node {
		constructor(data, next) {
		this.data = data;
	this.next = next;
	this.next = next \|\| null;
		}
		}

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