foo.cc: In function 'int main()':
foo.cc:121:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  121 |  for(int i = 0;i<v[0].size();i++)
      |                ~^~~~~~~~~~~~
foo.cc:125:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  125 |  for(int i = 0;i<v[1].size();i++)
      |                ~^~~~~~~~~~~~

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