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);
}
};