208. Implement Trie (Prefix Tree)

• categories: Code, Interview Question, leetcode, Medium
• source: https://leetcode.com/problems/implement-trie-prefix-tree
• topics: Trie

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.

class Trie:
 
    def __init__(self):
        self.trie = {}
 
    def insert(self, word: str) -> None:
        pointer = self.trie
        i = 0
        while i < len(word):
            if not word[i] in pointer:
                while i < len(word):
                    pointer[word[i]] = {}
                    pointer = pointer[word[i]]
                    i += 1
            else:
                pointer = pointer[word[i]]
                i += 1 
 
        if not "$" in pointer:
            pointer["$"] = True
                            
 
    def search(self, word: str) -> bool:
        pointer = self.trie
        for c in word:
            if c in pointer:
                pointer = pointer[c]
            else:
                return False
        return "$" in pointer
 
    def startsWith(self, prefix: str) -> bool:
        pointer = self.trie
        for c in prefix:
            if c in pointer:
                pointer = pointer[c]
            else:
                return False
        return True
 
 
# Your Trie object will be instantiated and called as such:
# obj = Trie()
# obj.insert(word)
# param_2 = obj.search(word)
# param_3 = obj.startsWith(prefix)