LeetCode Tries Prefix Tree

 class TrieNode {
 public:
     const static int NR_FANOUT = ;
     TrieNode* child[NR_FANOUT];
     int count;
     // Initialize your data structure here.
     TrieNode() {
         for (int i=; i<NR_FANOUT; i++) {
             child[i] = NULL;
         }
         count = ;
     }
 };

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

     // Inserts a word into the trie.
     void insert(string s) {
         insert(s, , root);
     }

     // Returns if the word is in the trie.
     bool search(string key) {
         return search(key, , root) != NULL;
     }

     // Returns if there is any word in the trie
     // that starts with the given prefix.
     bool startsWith(string prefix) {
         return search_prefix(prefix, , root) != NULL;
     }
 private:
     TrieNode* insert(string& s, int pos, TrieNode* current) {
         int len = s.size();
         if (pos > len) {
             return NULL;
         }
         if (current == NULL) {
             current = new TrieNode();
         }
         if (pos == len) {
             current->count++;
             return current;
         }
         int idx = s[pos] - 'a';
         current->child[idx] = insert(s, pos + , current->child[idx]);
         return current;
     }

     TrieNode* search(string& s, int pos, TrieNode* current) {
         if (current == NULL) {
             return NULL;
         }
         int len = s.size();
         if (pos > len) {
             return NULL;
         } else if (pos == len && current->count) {
             return current;
         }
         return search(s, pos + , current->child[s[pos] - 'a']);
     }
     TrieNode* search_prefix(string& s, int pos, TrieNode* current) {
         if (current == NULL) {
             return NULL;
         }
         int len = s.size();
         if (pos >= len) {
             return current;
         }
         return search_prefix(s, pos + , current->child[s[pos] - 'a']);
     }
 private:
     TrieNode* root;
 };

mplement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.