/in/foo.cc: In function 'int main()':
/in/foo.cc:36:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |                 for(int i=0; i<res.size(); i++)//输出
      |                              ~^~~~~~~~~~~
/in/foo.cc:38:39: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |                         for(int j=0; j<res[i].size(); j++)
      |                                      ~^~~~~~~~~~~~~~