trie.py

# 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.


class TrieNode:
    def __init__(self):
        self.children = {}
        self.end = False

class Trie:

    def __init__(self):
        self.root = TrieNode()

    def insert(self, word: str) -> None:
        node = self.root
        for char in word:
            if node.children.get(char):
                node = node.children[char]
            else:
                newnode = TrieNode()
                node.children[char] = newnode
                node = newnode
        node.end = True

    def find(self, word):
        node = self.root
        for char in word:
            if char in node.children:
                node = node.children[char]
            else:
                return None
        return node
        
    def search(self, word: str) -> bool:
        node = self.find(word)
        return node and node.end

    def startsWith(self, prefix: str) -> bool:
        return self.find(prefix)


# 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)