/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:10:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<G[u].size(); i++)
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:48:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0; j<G[i].size(); j++)
                ~^~~~~~~~~~~~