Implement Trie (Prefix Tree)

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

Note:
You may assume that all inputs are consist of lowercase letters a-z.

思路：应该就是字典树。

class TrieNode {
public:
    TrieNode *dic[27];
    // Initialize your data structure here.
    TrieNode() {
        for (int i = 0; i < 27; i++)
            dic[i] = NULL;
    }
};

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

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode* cur = root;
        for (int i = 0, len = word.size(); i < len; i++)
        {
            int loc = (int)(word[i] - 'a');
            if (cur->dic[loc] == NULL)
                cur->dic[loc] = new TrieNode();
            cur = cur->dic[loc];
        }
        if (cur->dic[26] == NULL)
            cur->dic[26] = new TrieNode();
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        TrieNode* cur = root;
        for (int i = 0, len = word.size(); i < len; i++)
        {
            int loc = (int)(word[i] - 'a');
            if (cur->dic[loc] == NULL) return false;
            cur = cur->dic[loc];
        }
        if (cur->dic[26] == NULL) return false;
        return true;
    }

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

private:
    TrieNode* root;
};

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