/in/foo.cc: In function 'void f1(std::vector<std::vector<int> >&, std::vector<int>&, int)':
/in/foo.cc:7:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int j = 0; j < A[0].size(); j++)
                  ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'int f(std::vector<std::vector<int> >&, std::vector<int>&)':
/in/foo.cc:20:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < A.size(); i++)
                  ~~^~~~~~~~~~