alg.rb

def qsort (arr, left=0, right=arr.length-1, pl=left, pr=right)
  x = arr[(left+right)/2]
  begin
    pl+=1 while arr[pl] < x
    pr-=1 while arr[pr] > x
    arr[pl], arr[pr] = arr[pr], arr[pl]
  end while arr[pl] != arr[pr]
  qsort(arr, left, pl-1) if pl-left > 1
  qsort(arr, pr+1, right) if right-pr > 1
end

arr =(1..10).sort_by {rand}
qsort(arr)
p "result:#{arr}"