Leetcode OJ : Restore IP Addresses backtrack暴搜 C++ solution

 class Solution {
     public:
     vector<string> ret;
     string src;
     int len;
     unordered_set<string> added;
     vector<string> restoreIpAddresses(string s) {
         if ( s.empty() )  return ret;
         src = s;
         len = src.size();
         backTrack(,,  "");
         return ret;
     }

     void backTrack(int pos, int dot_cnt, string substr) {
         if ( dot_cnt >  ) return;
         if ( pos >= len && dot_cnt ==  ) {
             substr.pop_back();
             if ( added.find(substr) == added.end() ) {
                 ret.push_back( substr );
                 added.insert( substr );
             }
             return;
         }
         char buffer[];
         int tx = len - pos >  ?  : len - pos;
         for ( int i = ; i <= tx; i++ ) {
             string temp = src.substr( pos, i );
             int number = atoi( temp.c_str() );
             sprintf( buffer, "%d", number );
             string str(buffer);
             if ( str != temp ) continue;
             string newsub = substr + temp + ".";
             if ( number >=  && number <=  ) {
                 backTrack( pos + i, dot_cnt + ,  newsub );
             }
         }
     }
 };