foo.cc: In function 'int main()':
foo.cc:15:11: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(scanf("%d",&$);$--;){
      ~~~~~^~~~~~~~~
foo.cc:16:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&n);
   ~~~~~^~~~~~~~~
foo.cc:19:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d",&x),e[x].push_back(i);
    ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~

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

{"receive":"2020-05-30T04:20:39.999Z","handle":"2020-05-30T04:20:39.999Z","cache_start":"2020-05-30T04:20:40.006Z","read_cases":"2020-05-30T04:20:42.283Z","judge":"2020-05-30T04:20:42.284Z","done":"2020-05-30T04:20:46.060Z"}