题目：

题解：

class Trie {
private:vector<Trie*> children;bool isEnd;Trie* searchPrefix(string prefix) {Trie* node = this;for (char ch : prefix) {ch -= 'a';if (node->children[ch] == nullptr) {return nullptr;}node = node->children[ch];}return node;}public:Trie() : children(26), isEnd(false) {}void insert(string word) {Trie* node = this;for (char ch : word) {ch -= 'a';if (node->children[ch] == nullptr) {node->children[ch] = new Trie();}node = node->children[ch];}node->isEnd = true;}bool search(string word) {Trie* node = this->searchPrefix(word);return node != nullptr && node->isEnd;}bool startsWith(string prefix) {return this->searchPrefix(prefix) != nullptr;}
};