/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:13:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<v[k].size(); i++) {
                ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:44:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j=0; j<v[i].size(); j++) {
                 ~^~~~~~~~~~~~