recursive function qsort(x) result(y) integer,intent(in) ::x(:) integer,allocatable::y(:) integer::pivot,total total = size(x) if (total <=1) then y = x else pivot = x(total/2) y = [qsort(pack(x, x .lt. pivot)), & pack(x, x .eq. pivot), & qsort(pack(x, x .gt. pivot))] endif end function qsort program main interface recursive function qsort(x) result(y) integer,intent(in) ::x(:) integer,allocatable::y(:) end function qsort end interface integer::N,i,kankaku integer,allocatable::x(:),y(:) read *, N allocate(x(N),y(N)) read *, x y = qsort(x) kankaku = y(2)-y(1) if(kankaku.eq.0) then print '(a)', "NO" return end if do i=2,N-1 if(y(i)+kankaku.ne.y(i+1)) then print '(a)', "NO" return end if end do print '(a)', "YES" end program