/in/foo.cc: In function 'void bfs()':
/in/foo.cc:17:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<G[1].size();i++) {
              ~^~~~~~~~~~~~
/in/foo.cc:23:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<G[x].size();i++) {
               ~^~~~~~~~~~~~