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

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

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实现：

class TrieNode {
public:
bool hasValue = false;
TrieNode** children;
// Initialize your data structure here.
TrieNode() {
children = new TrieNode*[26]();
}
~TrieNode() {
for (int i = 0; i < 26; i++) {
delete children[i];
}
delete children;
}
};

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

// Inserts a word into the trie.
void insert(string word) {
findNode(word, true)->hasValue = true;
}

// Returns if the word is in the trie.
bool search(string word) {
auto node = findNode(word, false);
return (node != nullptr && node->hasValue);
}

// Returns if there is any word in the trie
// that starts with the given prefix.
bool startsWith(string prefix) {
return findNode(prefix, false) != nullptr;
}

private:
TrieNode* findNode(const string &word, bool create) {
auto node = root;
int idx = 0;
for (int i = 0; i < word.size(); i++) {
idx = word[i] – ‘a’;
if (node->children[idx] == nullptr) {
if (create) {
node->children[idx] = new TrieNode();
}
else {
return nullptr;
}
}
node = node->children[idx];
}
return node;
}
TrieNode* root;
};