Leetcode 208 实现 Trie (前缀树)

实现 Trie (前缀树)

题目

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。

解答

class Trie:

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

    def insert(self, word: str) -> None:
        """
        Inserts a word into the trie.
        """
        # 从根节点出发
        node = self.root
        for char in word:
            if char not in node.children:  # 判断当前字符是否在当前节点的子节点里面，不在，则创建一个子节点
                node.children[char] = TreeNode()
            node = node.children[char]  # 跳到对应的子节点
        node.word = True

    def search(self, word: str) -> bool:
        """
        Returns if the word is in the trie.
        """
        node = self.root
        for char in word:
            if char not in node.children:
                return False
            node = node.children[char]
        return node.word

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

测试验证

class TreeNode:
    def __init__(self):
        self.word = False  # 表示当前节点是否是一个曾经插入的单词
        self.children = {}  # 子节点列表


class Trie:

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

    def insert(self, word: str) -> None:
        """
        Inserts a word into the trie.
        """
        # 从根节点出发
        node = self.root
        for char in word:
            if char not in node.children:  # 判断当前字符是否在当前节点的子节点里面，不在，则创建一个子节点
                node.children[char] = TreeNode()
            node = node.children[char]  # 跳到对应的子节点
        node.word = True

    def search(self, word: str) -> bool:
        """
        Returns if the word is in the trie.
        """
        node = self.root
        for char in word:
            if char not in node.children:
                return False
            node = node.children[char]
        return node.word

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


if __name__ == '__main__':
    obj = Trie()
    obj.insert("apple")
    print(obj.search("apple"), "= True")
    print(obj.search("app"), "= False")
    print(obj.startsWith("app"), "= True")
    obj.insert("app")
    print(obj.search("app"), "= True")