/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:44:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<q[u].size();i++)
               ~^~~~~~~~~~~~
/in/foo.cc:54:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<graph[u].size();i++) //u的邻居
               ~^~~~~~~~~~~~~~~~
/in/foo.cc: In function 'bool dfs2(int, int)':
/in/foo.cc:70:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<graph[u].size();i++)
               ~^~~~~~~~~~~~~~~~