Merge pull request knaxus#104 from knaxus/trie

Trie - tree based data structure

Author: TheSTL

README.md

@@ -31,17 +31,16 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
   - [Implement 2 Stacks using Single Array](src/_DataStructures_/Stack/2-stacks-using1-array)
   - [Sort a Stack](src/_DataStructures_/Stack/sort-a-stack)
 
-
-- [Queue](src/_DataStructures_/Queue)
+* [Queue](src/_DataStructures_/Queue)
 
   - [Weave](src/_DataStructures_/Queue/weave)
   - [Reverse First K Elements of a Queue](src/_DataStructures_/Queue/reverse-first-k)
   - [Generate all Binary Numbers from 1 to N](src/_DataStructures_/Queue/generate-binary-number)
   - [Queue using Stack](src/_DataStructures_/Queue/queue-using-stack)
 
-- [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
+* [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
 
-- [Trees](src/_DataStructures_/Trees)
+* [Trees](src/_DataStructures_/Trees)
   - [Binary Tree (creation using level order)](src/_DataStructures_/Trees/BinaryTree)
   - [Binary Search Tree](src/_DataStructures_/Trees/BinarySearchTree)
     - [Find k<sup>th</sup> maximum in a BinarySearchTree](src/_DataStructures_/Trees/BinarySearchTree/find-kth-max)
@@ -50,6 +49,7 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
     - [Find Height of BST](src/_DataStructures_/Trees/BinarySearchTree/height-of-bst)
     - [Find k Nodes from Root of BST](src/_DataStructures_/Trees/BinarySearchTree/find-k-nodes-from-root)
   - [Suffix Tree](src/_DataStructures_/SuffixTree)
+  - [Trie](src/_DataStructures_/Trees/Trie)
 
 ### Logical Problems
 

src/_DataStructures_/Trees/Trie/Node.js

@@ -0,0 +1,20 @@
+class TrieNode {
+  constructor(char) {
+    this.char = char;
+    this.children = [];
+    this.isEndOfWord = false;
+
+    // mark all the alphabets as null
+    for (let i = 0; i < 26; i += 1) this.children[i] = null;
+  }
+
+  markAsLeaf() {
+    this.isEndOfWord = true;
+  }
+
+  unmarkAsLeaf() {
+    this.isEndOfWord = false;
+  }
+}
+
+module.exports = TrieNode;

src/_DataStructures_/Trees/Trie/index.js

@@ -0,0 +1,73 @@
+const Node = require('./Node');
+
+class Trie {
+  constructor() {
+    this.root = new Node('');
+  }
+
+  // helper to get the index of a character
+  // eslint-disable-next-line class-methods-use-this
+  getIndexOfChar(char) {
+    return char.charCodeAt(0) - 'a'.charCodeAt(0);
+  }
+
+  insert(key) {
+    if (!key) {
+      return false;
+    }
+
+    // convert to lower case
+    // keys are basically words
+    const word = key.toLowerCase();
+    let currentNode = this.root;
+
+    for (let level = 0; level < word.length; level += 1) {
+      const index = this.getIndexOfChar(word[level]);
+      if (!currentNode.children[index]) {
+        currentNode.children[index] = new Node(word[level]);
+      }
+      currentNode = currentNode.children[index];
+    }
+
+    // when we are done with inserting all the character of the word,
+    // mark the node as end leaf
+    currentNode.markAsLeaf();
+    return true;
+  }
+
+  search(key) {
+    if (!key) {
+      return false;
+    }
+
+    // convert word to lower case
+    const word = key.toLowerCase();
+    let currentNode = this.root;
+
+    for (let level = 0; level < word.length; level += 1) {
+      const index = this.getIndexOfChar(word[level]);
+      if (!currentNode.children[index]) {
+        return false;
+      }
+      currentNode = currentNode.children[index];
+    }
+    if (currentNode !== null && currentNode.isEndOfWord) {
+      return true;
+    }
+    return false;
+  }
+}
+
+// const words = ['bed', 'ball', 'apple', 'java', 'javascript'];
+// const trie = new Trie();
+
+// words.forEach(word => trie.insert(word));
+
+// console.log(trie.root);
+
+// console.log(trie.search(words[3]));
+// console.log(trie.search('word'));
+// console.log(trie.search(words[4]));
+// console.log(trie.search('random'));
+
+module.exports = Trie;