Implement Trie (Prefix Tree)

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

 

Constraints:

• 1 <= word.length, prefix.length <= 2000
• word and prefix consist only of lowercase English letters.
• At most 3 * 104 calls in total will be made to insert, search, and startsWith.

Solution

class Node {
    constructor() {
        this.end = false;
        this.children = {};
    }
}

class Trie {
    constructor() {
        this.root = new Node();
    }

    insert(word) {
        let r = this.root;
        for (const c of word) {
            if (!(c in r.children)) {
                r.children[c] = new Node();
            }
            r = r.children[c];
        }
        r.end = true;
    }

    search(word) {
        let r = this.root;
        for (const c of word) {
            if (!(c in r.children)) {
                return false;
            }
            r = r.children[c];
        }
        return r.end;
    }

    startsWith(prefix) {
        let r = this.root;
        for (const c of prefix) {
            if (!(c in r.children)) {
                return false;
            }
            r = r.children[c];
        }
        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)
 */

We will create our trie using nested dictionaries (encapsulated as a Node) where the key is the character.