foo.cc: In function 'int main()':
foo.cc:20:17: warning: variable 'r' set but not used [-Wunused-but-set-variable]
         int l=0,r=1;
                 ^
foo.cc:16:21: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         int n; scanf("%d",&n);
                ~~~~~^~~~~~~~~
foo.cc:17:36: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         for(int i=1;i<=n;i++) scanf("%d",a+i);
                               ~~~~~^~~~~~~~~~

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

{"receive":"2020-07-20T08:47:25.703Z","handle":"2020-07-20T08:47:25.703Z","cache_start":"2020-07-20T08:47:25.710Z","read_cases":"2020-07-20T08:47:25.833Z","judge":"2020-07-20T08:47:25.834Z","done":"2020-07-20T08:47:27.152Z"}