Trie Added in JS (#296)

* Trie Added in JS

* Standard Fixed

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: Lakhan-Nad

DIRECTORY.md

@@ -42,6 +42,7 @@
     * [StackES6](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Stack/StackES6.js)
   * Tree
     * [BinarySearchTree](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Tree/BinarySearchTree.js)
+    * [Trie](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Tree/Trie.js)
 
 ## Dynamic-Programming
   * [CoinChange](https://github.com/TheAlgorithms/Javascript/blob/master/Dynamic-Programming/CoinChange.js)

Data-Structures/Tree/Trie.js

@@ -0,0 +1,137 @@
+var TrieNode = function TrieNode (key, parent) {
+  this.key = key
+  this.count = 0
+  this.children = Object.create(null)
+  if (parent === undefined) {
+    this.parent = null
+  } else {
+    this.parent = parent
+  }
+}
+
+function Trie () {
+  // create only root with null key and parent
+  this.root = new TrieNode(null, null)
+}
+
+// Recursively finds the occurence of all words in a given node
+Trie.findAllWords = function (root, word, output) {
+  if (root === null) return
+  if (root.count > 0) {
+    if (typeof output === 'object') { output.push({ word: word, count: root.count }) }
+  }
+  var key
+  for (key in root.children) {
+    word += key
+    this.findAllWords(root.children[key], word, output)
+    word = word.slice(0, -1)
+  }
+}
+
+Trie.prototype.insert = function (word) {
+  if (typeof word !== 'string') return
+  if (word === '') {
+    this.root.count += 1
+    return
+  }
+  var node = this.root
+  var len = word.length
+  var i
+  for (i = 0; i < len; i++) {
+    if (node.children[word.charAt(i)] === undefined) { node.children[word.charAt(i)] = new TrieNode(word.charAt(i), node) }
+    node = node.children[word.charAt(i)]
+  }
+  node.count += 1
+}
+
+Trie.prototype.findPrefix = function (word) {
+  if (typeof word !== 'string') return null
+  var node = this.root
+  var len = word.length
+  var i
+  // After end of this loop node will be at desired prefix
+  for (i = 0; i < len; i++) {
+    if (node.children[word.charAt(i)] === undefined) return null // No such prefix exists
+    node = node.children[word.charAt(i)]
+  }
+  return node
+}
+
+Trie.prototype.remove = function (word, count) {
+  if (typeof word !== 'string') return
+  if (typeof count !== 'number') count = 1
+  else if (count <= 0) return
+
+  // for empty string just delete count of root
+  if (word === '') {
+    if (this.root.count >= count) this.root.count -= count
+    else this.root.count = 0
+    return
+  }
+
+  var child = this.root
+  var len = word.length
+  var i, key
+  // child: node which is to be deleted
+  for (i = 0; i < len; i++) {
+    key = word.charAt(i)
+    if (child.children[key] === undefined) return
+    child = child.children[key]
+  }
+
+  // Delete no of occurences specified
+  if (child.count >= count) child.count -= count
+  else child.count = 0
+
+  // If some occurences are left we dont delete it or else
+  // if the object forms some other objects prefix we dont delete it
+  // For checking an empty object
+  // https://stackoverflow.com/questions/679915/how-do-i-test-for-an-empty-javascript-object
+  if (child.count <= 0 && (Object.keys(child.children).length && child.childre.constructor === Object)) {
+    child.parent.children[child.key] = undefined
+  }
+}
+
+Trie.prototype.findAllWords = function (prefix) {
+  var output = []
+  // find the node with provided prefix
+  var node = this.findPrefix(prefix)
+  // No such prefix exists
+  if (node === null) return output
+  Trie.findAllWords(node, prefix, output)
+  return output
+}
+
+Trie.prototype.contains = function (word) {
+  // find the node with given prefix
+  var node = this.findPrefix(word)
+  // No such word exists
+  if (node === null || node.count === 0) return false
+  return true
+}
+
+Trie.prototype.findOccurences = function (word) {
+  // find the node with given prefix
+  var node = this.findPrefix(word)
+  // No such word exists
+  if (node === null) return 0
+  return node.count
+};
+
+// To test
+(function demo () {
+  var x = new Trie()
+  x.insert('sheldon')
+  x.insert('hello')
+  x.insert('anyword')
+  x.insert('sheldoncooper')
+  console.log(x.findOccurences('sheldon'))
+  x.remove('anything')
+  x.insert('sheldon')
+  console.log(x.findOccurences('sheldon'))
+  console.log(x.findAllWords('sheldon'))
+  x.insert('anything')
+  x.remove('sheldoncooper')
+  console.log(x.contains('sheldoncooper'))
+  console.log(x.findAllWords('sheldon'))
+})()