struct TrieNode {
    bool isEnd;
    TrieNode* children[26];
<pre class='brush:php;toolbar:false;'>TrieNode() {
    isEnd = false;
    for (int i = 0; i < 26; ++i) {
        children[i] = nullptr;
    }
}

};

void insert(TrieNode* root, const string& word) {
    TrieNode* node = root;
    for (char ch : word) {
        int idx = ch - 'a';
        if (!node->children[idx]) {
            node->children[idx] = new TrieNode();
        }
        node = node->children[idx];
    }
    node->isEnd = true;
}

bool search(TrieNode* root, const string& word) {
    TrieNode* node = root;
    for (char ch : word) {
        int idx = ch - 'a';
        if (!node->children[idx]) {
            return false;
        }
        node = node->children[idx];
    }
    return node->isEnd;
}
</font><H3>查找前缀是否存在</H3><p>与查找字符串类似，但不需要判断isEnd。只要能完整遍历前缀的所有字符，就说明存在该前缀。</p><font color="#0000FF"><pre class="brush:php;toolbar:false;">
bool startsWith(TrieNode* root, const string& prefix) {
    TrieNode* node = root;
    for (char ch : prefix) {
        int idx = ch - 'a';
        if (!node->children[idx]) {
            return false;
        }
        node = node->children[idx];
    }
    return true;
}