Leetcode —— 208. 实现 Trie (前缀树)（Python）

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。

class Trie:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.trie = {}

    def insert(self, word: str) -> None:
        """
        Inserts a word into the trie.
        """
        root = self.trie
        for c in word:
            if c not in root:
                root[c] = {}
            root = root[c]
        root['word'] = word
		# 当插入apple时，得到的trie树为
		# {'a': {'p': {'p': {'l': {'e': {'word': 'apple'}}}}}}
		# 在trie树的最底部为字符串的整体表示

    def search(self, word: str) -> bool:
        """
        Returns if the word is in the trie.
        """
        root = self.trie
        for c in word:
            if c not in root:
                return False
            root = root[c]
        return 'word' in root.keys()
        # 在trie树的当前位置有"word"表示当前位置存在单词

    def startsWith(self, prefix: str) -> bool:
        """
        Returns if there is any word in the trie that starts with the given prefix.
        """
        root = self.trie
        for c in prefix:
            if c not in root:
                return False
            root = root[c]
        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)