foo.cc: In function 'int main()':
foo.cc:5:18: warning: unused variable 'b' [-Wunused-variable]
  int k,a[100005],b[10005],c[10005],d[10005],n1,n2,n3;
                  ^
foo.cc:5:27: warning: unused variable 'c' [-Wunused-variable]
  int k,a[100005],b[10005],c[10005],d[10005],n1,n2,n3;
                           ^
foo.cc:5:36: warning: unused variable 'd' [-Wunused-variable]
  int k,a[100005],b[10005],c[10005],d[10005],n1,n2,n3;
                                    ^
foo.cc:5:48: warning: unused variable 'n2' [-Wunused-variable]
  int k,a[100005],b[10005],c[10005],d[10005],n1,n2,n3;
                                                ^~
foo.cc:5:51: warning: unused variable 'n3' [-Wunused-variable]
  int k,a[100005],b[10005],c[10005],d[10005],n1,n2,n3;
                                                   ^~

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