【LeetCode】208.实现Trie(前缀树)

题目难度★★★

题目描述

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

题目地址 https://leetcode-cn.com/problems/implement-trie-prefix-tree

实现代码

class Trie {
public:
	/** Initialize your data structure here. */
	Trie(){
		root = new TrieNode();
	}

	/** Inserts a word into the trie. */
	void insert(string word) {
		TrieNode* p = root;
		for (auto& a : word) {
			int i = a - 'a';
			if (!p->child[i])
				p->child[i] = new TrieNode();
			p = p->child[i];
		}
		p->isWord = true;
	}

	/** Returns if the word is in the trie. */
	bool search(string word) {
		TrieNode* p = root;
		for (auto& a : word) {
			int i = a - 'a';
			if (!p->child[i])
				return false;
            p = p->child[i];
		}
		return p->isWord;
	}

	/** Returns if there is any word in the trie that starts with the given prefix. */
	bool startsWith(string prefix) {
		TrieNode* p = root;
		for (auto& a : prefix) {
			int i = a - 'a';
			if (!p->child[i])
				return false;
			p = p->child[i];
		}
		return true;
	}
private:
	struct TrieNode
	{
		TrieNode():isWord(false){
			for (auto &a:child)
			{
				a = NULL;
			}
		}

		TrieNode* child[26];
		bool isWord;
	};

	TrieNode* root;
};

/** * 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); */