foo.cc: In function 'int main()':
foo.cc:20:16: warning: unused variable 'b' [-Wunused-variable]
  int a[100000],b[100000],n,x,ans;
                ^
foo.cc:29:13: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<ans<<" ";
             ^~~

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