Add new hash table methods.

src/data-structures/hash-table/HashTable.js

@@ -1,14 +1,29 @@
 import LinkedList from '../linked-list/LinkedList';
 
+// Hash table size directly affects on the number of collisions.
+// The bigger the hash table size the less collisions you'll get.
+// For demonstrating purposes hash table size is small to show how collisions
+// are being handled.
 const defaultHashTableSize = 32;
 
 export default class HashTable {
+  /**
+   * @param {number} hashTableSize
+   */
   constructor(hashTableSize = defaultHashTableSize) {
     // Create hash table of certain size and fill each bucket with empty linked list.
     this.buckets = Array(hashTableSize).fill(null).map(() => new LinkedList());
+
+    // Just to keep track of all actual keys in a fast way.
+    this.keys = {};
   }
 
-  // Converts key string to hash number.
+  /**
+   * Converts key string to hash number.
+   *
+   * @param {string} key
+   * @return {number}
+   */
   hash(key) {
     const hash = Array.from(key).reduce(
       (hashAccumulator, keySymbol) => (hashAccumulator + keySymbol.charCodeAt(0)),
@@ -19,8 +34,14 @@ export default class HashTable {
     return hash % this.buckets.length;
   }
 
-  insert(key, value) {
-    const bucketLinkedList = this.buckets[this.hash(key)];
+  /**
+   * @param {string} key
+   * @param {*} value
+   */
+  set(key, value) {
+    const keyHash = this.hash(key);
+    this.keys[key] = keyHash;
+    const bucketLinkedList = this.buckets[keyHash];
     const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
 
     if (!node) {
@@ -32,8 +53,14 @@ export default class HashTable {
     }
   }
 
+  /**
+   * @param {string} key
+   * @return {*}
+   */
   delete(key) {
-    const bucketLinkedList = this.buckets[this.hash(key)];
+    const keyHash = this.hash(key);
+    delete this.keys[key];
+    const bucketLinkedList = this.buckets[keyHash];
     const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
 
     if (node) {
@@ -43,10 +70,29 @@ export default class HashTable {
     return null;
   }
 
+  /**
+   * @param {string} key
+   * @return {*}
+   */
   get(key) {
     const bucketLinkedList = this.buckets[this.hash(key)];
     const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
 
     return node ? node.value.value : null;
   }
+
+  /**
+   * @param {string} key
+   * @return {boolean}
+   */
+  has(key) {
+    return Object.hasOwnProperty.call(this.keys, key);
+  }
+
+  /**
+   * @return {string[]}
+   */
+  getKeys() {
+    return Object.keys(this.keys);
+  }
 }