LeetCode—Python—208. 实现 Trie (前缀树)

一、题目描述

Trie（208）：https://leetcode.com/problems/implement-trie-prefix-tree/description/

实现一个 Trie (前缀树)，包含 insert, search, 和 startsWith 这三个操作。

示例:

Trie trie = new Trie();

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

说明:

• 你可以假设所有的输入都是由小写字母 a-z 构成的。
• 保证所有输入均为非空字符串。

 

二、代码详解

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


class Trie:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.root = TrieNode()
        

    def insert(self, word: str) -> None:
        """
        Inserts a word into the trie.
        """
        current = self.root
        for letter in word:
            current = current.children[letter]
        current.is_word = True

    def search(self, word: str) -> bool:
        """
        Returns if the word is in the trie.
        """
        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: str) -> bool:
        """
        Returns if there is any word in the trie that starts with the given 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:
# obj = Trie()
# obj.insert(word)
# param_2 = obj.search(word)
# param_3 = obj.startsWith(prefix)