foo.cc: In function 'void dfs1(int)':
foo.cc:21:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<g1[x].size();i++)
              ~^~~~~~~~~~~~~
foo.cc: In function 'void dfs2(int)':
foo.cc:33:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<g2[x].size();i++)
              ~^~~~~~~~~~~~~
foo.cc: In function 'void shrink()':
foo.cc:64:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
      for(int i = 0;i<g1[x].size();i++)
                    ~^~~~~~~~~~~~~
foo.cc: In function 'void dfs(int)':
foo.cc:78:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<g4[x].size();i++)
              ~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:87:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&n, &m);
  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:100:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d",&a, &b);
   ~~~~~^~~~~~~~~~~~~~~~

自豪的采用 HydroJudger 进行评测(github.com/hydro-dev/HydroJudger)

{"receive":"2020-06-25T09:34:20.010Z","handle":"2020-06-25T09:34:20.010Z","cache_start":"2020-06-25T09:34:20.018Z","read_cases":"2020-06-25T09:34:20.151Z","judge":"2020-06-25T09:34:20.152Z","done":"2020-06-25T09:34:20.885Z"}