/in/foo.cc: In function 'void dfs1(int)':
/in/foo.cc:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<v1[id].size();i++)
              ~^~~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int)':
/in/foo.cc:16:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<v2[id].size();i++)
              ~^~~~~~~~~~~~~~