Trie树

记住Trie树的基本数据结构就可以了。

https://discuss.leetcode.com/topic/15581/80ms-clear-c-code-with-detailed-explanations

class TrieNode {
public:
    bool isKey;
    TrieNode* children[26];
    TrieNode(): isKey(false) {
        memset(children, NULL, sizeof(TrieNode*) * 26); 
    }
};