foo.cc: In function 'void Output(std::vector<std::vector<int> >&)':
foo.cc:6:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    6 |  for(int i=0; i<M.size(); i++)
      |               ~^~~~~~~~~
foo.cc:8:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |   for(int j=0; j<M[i].size(); j++)
      |                ~^~~~~~~~~~~~
foo.cc: In function 'void SortAll(std::vector<std::vector<int> >&)':
foo.cc:21:6: error: 'j' was not declared in this scope
   21 |   M[(j+1)/n][(j+1)%n] = tmp;
      |      ^

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