Leetcode 208.實現 Trie (前綴樹)（Implement Trie (Prefix Tree)）

Leetcode 208.實現 Trie (前綴樹)

1 題目描述（Leetcode題目鏈接）

  實現一個 Trie (前綴樹)，包含 insert, search, 和 startsWith 這三個操作。

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

說明:

• 你可以假設所有的輸入都是由小寫字母 a-z 構成的。
• 保證所有輸入均爲非空字符串。

2 題解

  字典樹基本操作的實現。

class TreeNode:
    def __init__(self):
        self.children = collections.defaultdict(TreeNode)
        self.end = False

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.
        """
        node = self.root
        for char in word:
            node = node.children[char]
        node.end = True


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


    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:
            node = node.children.get(char)
            if not node:
                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)