208. 实现 Trie (前缀树)

 

labuladong 题解

难度中等1194

Trie（发音类似 "try"）或者说 前缀树 是一种树形数据结构，用于高效地存储和检索字符串数据集中的键。这一数据结构有相当多的应用情景，例如自动补完和拼写检查。

请你实现 Trie 类：

• Trie() 初始化前缀树对象。
• void insert(String word) 向前缀树中插入字符串 word 。
• boolean search(String word) 如果字符串 word 在前缀树中，返回 true（即，在检索之前已经插入）；否则，返回 false 。
• boolean startsWith(String prefix) 如果之前已经插入的字符串 word 的前缀之一为 prefix ，返回 true ；否则，返回 false 。

 

示例：

输入
["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
输出
[null, null, true, false, true, null, true]

解释
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

class Trie:

    def __init__(self):
        self.children = [None]*26
        self.is_end = False

    def insert(self, word: str) -> None:
        node = self
        for ch in word:
            ii = ord(ch) - ord('a')
            if node.children[ii] == None:
                node.children[ii] = Trie()
            node = node.children[ii]
        node.is_end = True

    def search(self, word: str) -> bool:
        node = self
        for ch in word:
            ii = ord(ch) - ord('a')
            if node.children[ii] == None:
                return False
            node = node.children[ii]
        return node.is_end

    def startsWith(self, prefix: str) -> bool:
        node = self
        for ch in prefix:
            ii = ord(ch) - ord('a')
            if node.children[ii] == None:
                return False
            node = node.children[ii]
        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)

 

class Trie {
    std::vector<Trie*> children;
    bool is_end;
public:
    Trie() {
        is_end = false;
        children = std::vector<Trie*>(26);
    }
    
    void insert(string word) {
        Trie* node = this;
        for(auto ch : word) {
            if (node->children[ch-'a'] == nullptr) {
                node->children[ch-'a'] = new Trie();
            }
            node = node->children[ch-'a'];
        }
        node->is_end = true;
    }
    
    bool search(string word) {
        Trie* node = this;
        for(auto ch : word) {
            if (node->children[ch - 'a'] == nullptr) {
                return false;
            }
            node = node->children[ch-'a'];
        }
        return node->is_end;
    }
    
    bool startsWith(string prefix) {
        Trie* node = this;
        for(auto ch : prefix) {
            if (node->children[ch - 'a'] == nullptr) {
                return false;
            }
            node = node->children[ch - 'a'];
        }
        return true;
    }
};

/**
 * Your Trie object will be instantiated and called as such:
 * Trie* obj = new Trie();
 * obj->insert(word);
 * bool param_2 = obj->search(word);
 * bool param_3 = obj->startsWith(prefix);
 */