LeetCode Implement Trie (Prefix Tree)

class Trie {
	class Node{
		Node() :next(26, nullptr), m_IsEnd(false){
		}

		bool  m_IsEnd;
		vector<Node*> next;
	};
public:
	/** Initialize your data structure here. */
	Trie() {

	}

	/** Inserts a word into the trie. */
	void insert(string word) {
		Node* tn = &m_Head;
		int c;
		for (auto i : word) {
			//c = word2Int(i);
			c = i - 'a';
			if (tn->next[c] == nullptr) {
				tn->next[c] = new Node();
			}
			tn = (tn->next[c]);
		}
		tn->m_IsEnd = true;
	}

	/** Returns if the word is in the trie. */
	bool search(string word) {
		Node *tn = &m_Head;
		int c;
		for (auto i : word) {
			//c = word2Int(i);
			c = i - 'a';
			if (tn->next[c] == nullptr) {
				return false;
			}
			tn = tn->next[c];
		}
		return tn->m_IsEnd;
	}

	/** Returns if there is any word in the trie that starts with the given prefix. */
	bool startsWith(string prefix) {
		Node *tn = &m_Head;
		int c;
		for (auto i : prefix) {
			//c = word2Int(i);
			c = i - 'a';
			if (tn->next[c] == nullptr) {
				return false;
			}
			tn = tn->next[c];
		}
		return true;
	}

private:
	inline int word2Int(char c) {
		return c - 'a';
	}
private:
	Node m_Head;
};