LeetCode OJ：Implement Trie (Prefix Tree)（实现一个字典树(前缀树)）

Implement a trie with insert, search, and startsWith methods.

实现字典树，前面好像有道题做过类似的东西，代码如下：

class TrieNode {
public:
    // Initialize your data structure here.
    TrieNode():isLeaf(false)
    {
        for(auto & t : dic){
            t = NULL;
        }
    }
    TrieNode * dic[26];
    bool isLeaf;
};

class Trie {
public:
    Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode * p = root;
        for(int i = 0; i < word.size(); ++i){
            int index = word[i] - 'a';
            if(p->dic[index] == NULL)
                p->dic[index] = new TrieNode();
            p = p->dic[index];
        }
        p->isLeaf = true;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        TrieNode * p = root;
        for(int i = 0; i < word.size(); ++i){
            int index = word[i] - 'a';
            if(p->dic[index] == NULL)
                return false;
            p = p->dic[index];
        }
        return p->isLeaf;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        TrieNode * p = root;
        for(int i = 0; i < prefix.size(); ++i){
            int index = prefix[i] - 'a';
            if(p->dic[index] == NULL)
                return false;
            p = p->dic[index];
        }
        return true;
    }

private:
    TrieNode* root;
};

// Your Trie object will be instantiated and called as such:
// Trie trie;
// trie.insert("somestring");
// trie.search("key");