Leetcode #208 Simple Trie Implementation

Trie.cpp

class Trie {
private:    
    class TrieNode{  
    public:
        bool isWord;
        vector<TrieNode*> next;
        
        TrieNode() : next(vector<TrieNode*>(26, NULL)), isWord(false){}
        ~TrieNode(){
            for(auto node: next) delete node;
        } 
    };
    
    TrieNode* root;
    
public:
    /** Initialize your data structure here. */
    Trie() {
        root = new TrieNode();
    }
    
    ~Trie(){
        delete root;
    }
    
    /** Inserts a word into the trie. */
    void insert(string word) {
        TrieNode* p = root;
        
        for(int i = 0; i < word.length(); i++){
            char c = word[i];
            
            if(p->next[c - 'a'] == NULL) p->next[c - 'a'] = new TrieNode();
            p = p->next[c - 'a'];
        }
        
        p->isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode* p = find(word);
        
        return p != NULL && p->isWord;
    }
    
    TrieNode* find(string word){
        TrieNode* p = root;
        
        for(int i = 0; i < word.length() && p != NULL; i++){
            char c = word[i];
            p = p->next[c - 'a'];
        }
        
        return p;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        return find(prefix) != NULL;
    }
    
};