foo.cc: In function 'void Output(std::vector<std::vector<int> >&)':
foo.cc:6:23: 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:8:31: 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++)
      |                              ~^~~~~~~~~~~~

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