void reverseWords(string &s) {

         vector<string> words;

         int start = -;

         int len = ;

         for (int i = ; i < s.length(); i++) {

             if (s[i] == ' ') {

                 if (len > )

                     words.push_back(s.substr(start, len));

                 len = ;

             }

             else {

                 if (len == ) {

                     start = i;

                     len = ;

                 }

                 else

                     len++;

             }

         }

         if (len > )

             words.push_back(s.substr(start, len));

         string res;

         if (words.size() > ) {

             for (int i = words.size() - ; i > ; i--)

                 res += words[i] + " ";

             res += words[];

         }

         s = res;

 }