LeetCode 208. Implement Trie (Prefix Tree)

题目

Implement a trie with insert, search, and startsWith methods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

思路

字典树。

代码

class Node(object):
    def __init__(self):
        self.children = collections.defaultdict(Node)
        self.isword = False
        
        
class Trie(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.root = Node()
        
    def insert(self, word):
        """
        Inserts a word into the trie.
        :type word: str
        :rtype: None
        """
        current = self.root
        for w in word:
            current = current.children[w]
        current.isword = True

    def search(self, word):
        """
        Returns if the word is in the trie.
        :type word: str
        :rtype: bool
        """
        current = self.root
        for w in word:
            current = current.children.get(w)
            if current == None:
                return False
        return current.isword

    def startsWith(self, prefix):
        """
        Returns if there is any word in the trie that starts with the given prefix.
        :type prefix: str
        :rtype: bool
        """
        current = self.root
        for p in prefix:
            current = current.children.get(p)
            if current == None:
                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)