foo.cc: In function 'void dfs_(int, int, int)':
foo.cc:12:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<G[v].size();i++)
                 ~^~~~~~~~~~~~
foo.cc: In function 'void dfs(int, int)':
foo.cc:66:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<G[now].size();i++){
              ~^~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:93:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&x,&y);
     ~~~~~^~~~~~~~~~~~~~
foo.cc:110:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&x,&y);
     ~~~~~^~~~~~~~~~~~~~

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

{"receive":"2020-06-14T13:25:48.329Z","handle":"2020-06-14T13:25:48.329Z","cache_start":"2020-06-14T13:25:48.337Z","read_cases":"2020-06-14T13:25:48.480Z","judge":"2020-06-14T13:25:48.482Z","done":"2020-06-14T13:25:54.551Z"}