Implement Trie (Prefix Tree)

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Problem

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.

• boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.

• boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.

Example 1:

Input
["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
Output
[null, null, true, false, true, null, true]
Explanation
Trie trie = new Trie();
trie.insert("apple");
trie.search("apple");   // return True
trie.search("app");     // return False
trie.startsWith("app"); // return True
trie.insert("app");
trie.search("app");     // return True

Pseudocode

- implement a trie, the trick is to remember that objects are passed as reference
    - create a variable node that serves like a pointer
    - keep advancing node to newest node while building trie
    - terminate with isTerminal = true
                                ***MAGIC***
                *** node = node[word[i]] = node[word[i]] || {} ***

Solution

var Trie = function () {
  this.root = {};
};

/**
 * @param {string} word
 * @return {void}
 */
// from solutions
// https://leetcode.com/problems/implement-trie-prefix-tree/solutions/58870/concise-javascript-solution/
Trie.prototype.insert = function (word) {
  let node = this.root;

  for (let i = 0; i < word.length; i++) {
    // node is an object with a key word[i] and value word[i] or an empty object
    // ******* this works because objects in Javascript are passed as reference *******
    // reassigning node does not change the value of node, but moves node further into the nested array, think of it as moving node.next
    // {a: {} }
    // {a: {p: {}}} ==> node is now referencing the inner object node[p]
    // node = node[word[i]] = node[word[i]] || {}
    // also written as

    if (!node[word[i]]) {
      //key -----> value
      node[word[i]] = {};

      // reassigning node with the key node[word[i]] and value of an empty array
      node = node[word[i]];
    } else {
      //key -----> value
      node[word[i]] = node[word[i]];
      node = node[word[i]];
    }

    if (i === word.length - 1) {
      node.isTerminal = true;
    }
  }
};

/**
 * @param {string} word
 * @return {boolean}
 */
Trie.prototype.search = function (word, isPrefix) {
  let node = this.root;
  for (let c of word) {
    if (!node[c]) return false;
    node = node[c];
  }
  return isPrefix || !!node.isTerminal;
};

/**
 * @param {string} prefix
 * @return {boolean}
 */
Trie.prototype.startsWith = function (prefix) {
  return this.search(prefix, true);
};

Time and Space Complexity

Time

• What did the code do

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Space

• What did the code do

• Total -