foo.cc: In function 'int main()':
foo.cc:33:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<graph[now].size(); i++) {
                ~^~~~~~~~~~~~~~~~~~
foo.cc:14:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&n,&m);
  ~~~~~^~~~~~~~~~~~~~~
foo.cc:17:8: 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 HydroJudge 进行评测(github.com/hydro-dev/HydroJudge)

{"receive":"2020-07-11T13:42:05.735Z","handle":"2020-07-11T13:42:05.735Z","cache_start":"2020-07-11T13:42:05.742Z","read_cases":"2020-07-11T13:42:05.859Z","judge":"2020-07-11T13:42:05.860Z","done":"2020-07-11T13:42:06.335Z"}