(*
  A QuickSort function for int lists.
  Stephen Freund
  cs334
*)

(* Always include these at the top of your SML files so 
   large datatype values and lists will print fully *)
Control.Print.printDepth := 100;
Control.Print.printLength := 100;

(* 
   Partition: int * int list -> int list * int list
   Partition list around the pivot, and return the lists
   of smaller and larger elements. 
*)
fun partition (pivot, nil) = (nil, nil)
  | partition (pivot, x::xs) =
      let val (smaller, bigger) = partition (pivot, xs) 
      in
	if x < pivot then (x::smaller, bigger) 
	       	     else (smaller, x::bigger)
      end;

(* 
   qsort: int list -> int list
   Sort a list of integers using quick sort. 
*)
fun qsort (nil) = nil
  | qsort (p::rest) = 
      let val (smaller, bigger) = partition(p,rest)
      in
	qsort(smaller) @ [p] @ qsort(bigger)
      end;

qsort [6,23,6,3,78,23,12,6,7,34,7,1,23,7,23,6,3,6];