0208: Implement Trie (Prefix Tree)

Problem Statement

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.

Code Solution

class TNode:
    def __init__(self, val):
        self.val = val
        self.end = False
        self.children = {}
        
class Trie:
    def __init__(self):
        self.root = TNode('')
        
    def insert(self, word):
        temp = self.root
        for cx, c in enumerate(word):
            if c not in temp.children:
                temp.children[c] = TNode(c)
            temp = temp.children[c]
        temp.end = True
    
    def search(self, word):
        temp = self.root
        for c in word:
            if c not in temp.children:
                return False
            temp = temp.children[c]
        return temp.end
	    
    def startsWith(self, prefix):
        temp = self.root
        for c in prefix:
            if c not in temp.children:
                return False
            temp = temp.children[c]
        return True