foo.cc: In function 'void dfs(int, int)':
foo.cc:17:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<G[now].size();i++){
              ~^~~~~~~~~~~~~~

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

{"receive":"2020-06-14T13:14:15.822Z","handle":"2020-06-14T13:14:15.822Z","cache_start":"2020-06-14T13:14:15.829Z","read_cases":"2020-06-14T13:14:15.963Z","judge":"2020-06-14T13:14:15.964Z","done":"2020-06-14T13:14:18.709Z"}