208. Implement Trie (Prefix Tree)

class TrieNode {
public:
    TrieNode* child[26];
    bool isWord = false;
    TrieNode()
    {
        for (int i = 0; i < 26; ++i)
        {
            child[i] = nullptr;
        }
    }
};

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

    void insert(string word)
    {
        TrieNode* node = root;
        for (auto w : word)
        {
            if (!node->child[w - 'a'])
            {
                node->child[w - 'a'] = new TrieNode();
            }
            node = node->child[w - 'a'];
        }
        node->isWord = true;
    }

    bool search(string word)
    {
        TrieNode* node = root;
        for (auto w : word)
        {
            if (!node->child[w - 'a']) return false;
            node = node->child[w - 'a'];
        }
        return node->isWord;
    }

    bool startsWith(string prefix)
    {
        TrieNode* node = root;
        for (auto p : prefix)
        {
            if (!node->child[p - 'a']) return false;
            node = node->child[p - 'a'];
        }
        return true;
    }
};

/**
 * Your Trie object will be instantiated and called as such:
 * Trie* obj = new Trie();
 * obj->insert(word);
 * bool param_2 = obj->search(word);
 * bool param_3 = obj->startsWith(prefix);
 */

• T: $O(N)$
• S: $O(N)$