#1804 - Implement Trie II (Prefix Tree)

Problem Description

A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.

Implement the Trie class:

Trie() Initializes the trie object.
void insert(String word) Inserts the string word into the trie.
int countWordsEqualTo(String word) Returns the number of instances of the string word in the trie.
int countWordsStartingWith(String prefix) Returns the number of strings in the trie that have the string prefix as a prefix.
void erase(String word) Erases the string word from the trie.

Solution

var Trie = function() {
  this.root = { children: {}, wordCount: 0, prefixCount: 0 };
};

/**
 * @param {string} word
 * @return {void}
 */
Trie.prototype.insert = function(word) {
  let currentNode = this.root;
  for (const char of word) {
    if (!currentNode.children[char]) {
      currentNode.children[char] = { children: {}, wordCount: 0, prefixCount: 0 };
    }
    currentNode = currentNode.children[char];
    currentNode.prefixCount++;
  }
  currentNode.wordCount++;
};

/**
 * @param {string} word
 * @return {number}
 */
Trie.prototype.countWordsEqualTo = function(word) {
  let currentNode = this.root;
  for (const char of word) {
    if (!currentNode.children[char]) {
      return 0;
    }
    currentNode = currentNode.children[char];
  }
  return currentNode.wordCount;
};

/**
 * @param {string} prefix
 * @return {number}
 */
Trie.prototype.countWordsStartingWith = function(prefix) {
  let currentNode = this.root;
  for (const char of prefix) {
    if (!currentNode.children[char]) {
      return 0;
    }
    currentNode = currentNode.children[char];
  }
  return currentNode.prefixCount;
};

/**
 * @param {string} word
 * @return {void}
 */
Trie.prototype.erase = function(word) {
  let currentNode = this.root;
  for (const char of word) {
    currentNode = currentNode.children[char];
    currentNode.prefixCount--;
  }
  currentNode.wordCount--;
};