string longestCommonPrefix(vector<string>& strs) {
        string pre = "";
        string sentinel = *min_element(strs.begin(), strs.end());
        for(int i=0; i< sentinel.size(); ++i){
            pre += strs.at(0).at(i);
          for(int j=1; j< strs.size(); ++j){
              if(strs.at(j).at(i) != pre.at(pre.size()-1)){
                 pre.pop_back();
                  return pre;
              }
          }
        }
        return pre;
    } ```