Leetcode 208 - Implement Trie

Note:

  • What does Trie look like?
    img
  • children must be defined as an object so we can quickly check if a char is presented using children[char].
  • While inserting, we have to specify isEnd to the last char. Because only in this way, we can tell the difference between app and apple. Otherwise, we won’t be sure if appl is also presented in our Trie.

Question:

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:

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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

Code:

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

/**
* @param {string} word
* @return {void}
*/
Trie.prototype.insert = function(word) {
let node = this.children;
for (let char of word) {
if (!node[char]) {
node[char] = {};
}
node = node[char];
}
node.isEnd = true;
};

/**
* @param {string} word
* @return {boolean}
*/
Trie.prototype.search = function(word) {
let node = this.children;
for (let char of word) {
if (!node[char]) return false;
node = node[char];
}
return node.isEnd === true;
};

/**
* @param {string} prefix
* @return {boolean}
*/
Trie.prototype.startsWith = function(prefix) {
let node = this.children;
for (let char of prefix) {
if (!node[char]) return false;
node = node[char];
}
return true;
};

/**
* Your Trie object will be instantiated and called as such:
* var obj = new Trie()
* obj.insert(word)
* var param_2 = obj.search(word)
* var param_3 = obj.startsWith(prefix)
*/