update: initial skeleton for Hash Table

Author: ashokdey

src/_DataStructures_/HashTable/HashEntry.js

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

src/_DataStructures_/HashTable/index.js

@@ -0,0 +1,109 @@
+const { Node } = require('../LinkedList');
+
+class HashTable {
+  constructor(slots) {
+    // init with a default set of slots
+    this.slot = slots || 17;
+    // size to hold the current size
+    // and help to resize when the table is half filled
+    this.size = 0;
+    // the main bucket
+    this.bucket = new Array(this.slot);
+
+    // 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 = 1801;
+
+    // loop till the length of the key or mamx 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 + value) % this.bucket.length;
+    }
+    return index;
+  }
+
+  _push(index, value) {
+    /**
+     * Util to add a SSL to the index in case of more than once
+     * value for the same key exixts
+     */
+    const node = new Node(value);
+    if (!this.bucket[index]) {
+      this.bucket[index] = node;
+      this.size += 1;
+      return index;
+    }
+
+    let head = this.bucket[index];
+
+    // traverse to the end
+    while (head.next !== null) {
+      head = head.next;
+    }
+    head.next = node;
+    this.size += 1;
+    return index;
+  }
+
+  _values(index, key) {
+    /**
+     * Util to return the values as an array
+     */
+    const res = [];
+    let head = this.bucket[index];
+    while (head !== null) {
+      if (head.data.key === key) {
+        res.push(head.data.value);
+      }
+      head = head.next;
+    }
+    return res;
+  }
+
+  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 });
+  }
+
+  get(key) {
+    // get the index
+    // 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._values(index, key);
+  }
+
+  getSize() {
+    return this.size;
+  }
+
+  isEmpty() {
+    return this.getSize() === 0;
+  }
+}
+
+// const ht = new HashTable();
+// ht.set('hello', 'I am a new value');
+// ht.set('hello', 'I am a yet another value');
+// ht.set('maroon', 'I maroon');
+// ht.set('yellow', 'I am yellow');
+
+// console.log(ht.get('hello'));
+// console.log(ht.get('maroon'));
+// console.log(ht.bucket);
+
+module.exports = HashTable;

src/_DataStructures_/LinkedList/index.js

@@ -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;
   }
 }