/in/foo.cc: In function 'void dfs1(int, int)':
/in/foo.cc:20:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<E[x].size();i++)
              ~^~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int)':
/in/foo.cc:35:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<E[x].size();i++)
              ~^~~~~~~~~~~~