Trie.js

import TrieNode from './TrieNode';

// Character that we will use for trie tree root.
const HEAD_CHARACTER = '*';

export default class Trie {
  constructor() {
    this.head = new TrieNode(HEAD_CHARACTER);
  }

  /**
   * @param {string} word
   * @return {Trie}
   */
  addWord(word) {
    const characters = Array.from(word);
    let currentNode = this.head;

    for (let charIndex = 0; charIndex < characters.length; charIndex += 1) {
      const isComplete = charIndex === characters.length - 1;
      currentNode = currentNode.addChild(characters[charIndex], isComplete);
    }

    return this;
  }

  /**
   * @param {string} word
   * @return {string[]}
   */
  suggestNextCharacters(word) {
    const lastCharacter = this.getLastCharacterNode(word);

    if (!lastCharacter) {
      return null;
    }

    return lastCharacter.suggestChildren();
  }

  /**
   * @param {string} word
   * @return {boolean}
   */
  doesWordExist(word) {
    return !!this.getLastCharacterNode(word);
  }

  /**
   * @param {string} word
   * @return {TrieNode}
   */
  getLastCharacterNode(word) {
    const characters = Array.from(word);
    let currentNode = this.head;

    for (let charIndex = 0; charIndex < characters.length; charIndex += 1) {
      if (!currentNode.hasChild(characters[charIndex])) {
        return null;
      }

      currentNode = currentNode.getChild(characters[charIndex]);
    }

    return currentNode;
  }
}