[LeetCode] Implement Trie (Prefix Tree)

You need to understand what a Trie is before writing the code :-) This link has a nice solution, whose code is rewritten below.

class TrieNode {
public:
    bool isWord;
    TrieNode* children[26];
    // Initialize your data structure here.
    TrieNode() : isWord(false) {
        memset(children, NULL, sizeof(TrieNode*) * 26);
    }
};

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

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode* run = root;
        for (char c : word) {
            if (!(run -> children[c - 'a']))
                run -> children[c - 'a'] = new TrieNode();
            run = run -> children[c - 'a'];
        }
        run -> isWord = true;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        TrieNode* p = query(word);
        return p && p -> isWord;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        return query(prefix);
    }

private:
    TrieNode* root;
    TrieNode* query(string& s) {
        TrieNode* run = root;
        for (char c : s) {
            if (!(run -> children[c - 'a'])) return NULL;
            run = run -> children[c - 'a'];
        }
        return run;
    }
};

// Your Trie object will be instantiated and called as such:
// Trie trie;
// trie.insert("somestring");
// trie.search("key");