/in/foo.cc: In function 'void dfs1(int, int)':
/in/foo.cc:31:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<G[u].size();i++)
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int)':
/in/foo.cc:52:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<G[u].size();i++)
               ~^~~~~~~~~~~~