/in/foo.cc: In function 'void DFS(int, std::vector<int>, int, std::vector<std::vector<int> >&)':
/in/foo.cc:13:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (cur > n || a.size() > n)
                 ~~~~~~~~~^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:32:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < res.size(); i++)
                  ~~^~~~~~~~~~~~
/in/foo.cc:34:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < res[i].size(); j++)
                   ~~^~~~~~~~~~~~~~~