bool wordBreak(string s, unordered_set<string> &dict) {

         int maxLen = ;

         for (auto w : dict)

             maxLen = maxLen > w.length() ? maxLen : w.length();

         vector<bool> res(s.length() + , false);

         res[s.length()] = true;

         for (int i = s.length() - ; i >= ; i--) {

             for (int l = ; !res[i] && l <= maxLen && i + l <= s.length(); l++)

                 res[i] = dict.find(s.substr(i, l)) != dict.end() && res[i + l];

         }

         return res[];

 }