208. Implement Trie (Prefix Tree).py

import collections

class TrieNode:
# Initialize your data structure here.
    def __init__(self):
        self.children = collections.defaultdict(TrieNode)
        self.is_word = False    #end of one word

class Trie:

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

    def insert(self, word):
        current = self.root
        for letter in word:
            current = current.children[letter]
        current.is_word = True

    def search(self, word):
        current = self.root
        for letter in word:
            current = current.children.get(letter)
            if current is None:
                return False
        return current.is_word

    def startsWith(self, prefix):
        current = self.root
        for letter in prefix:
            current = current.children.get(letter)
            if current is None:
                return False
        return True

# Your Trie object will be instantiated and called as such:
trie = Trie();
trie.insert("apple");
print trie.startsWith("ap"); # returns true