foo.cc: In function 'int main()':
foo.cc:64:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   64 |                 for (int j = 0; j < c[i].size(); j ++ )
      |                                 ~~^~~~~~~~~~~~~

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