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From: Hans-Malte Kern <kernhe@mickey.informatik.uni-stuttgart.de>
Subject: Re: Quicksort
Date: 1998/07/29
Message-ID: 
 <Pine.HPP.3.93.980729151224.6744A-100000@mickey.informatik.uni-stuttgart.de>#1/1
X-Deja-AN: 375990379
References: <01bdbaef$d13c9340$86eba8c2@j.couston>
To: Jamie <j.couston@virgin.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII
Organization: Informatik, Uni Stuttgart, Germany
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Newsgroups: comp.lang.ada
Date: 1998-07-29T00:00:00+00:00
List-Id: <comp.lang.ada>

On 29 Jul 1998, Jamie wrote:

On 29 Jul 1998, Jamie wrote:

> Hi,
>
> I was wondering if anyone could help me out with some source code. I wish
> to see a simple implementation of the Quicksort algorithm. As I'm still 
> a newcomer to Ada It would only have to deal with arrays of positive
> integers - but please can you make it a recursive NOT iterative process.

This one is taken from our informatic lecture

procedure Q_Sort(Field: in out Field_Type) is
 procedure Local_Q_Sort(L, R: in Index_Typ) is
  Left, Right: Integer range Field'First-1 .. Field'Last-1;
  Pivot: Element_Type;   
 begin
   Left:=L;
   Right:=R;
   Pivot:=Field((L+R)/2); --just take the midde
   while Left =< Right loop
     while Field(Left) < Pivot loop
       Left:=Left+1;
     end loop;
     while Field(Right) > Pivot loop
       Right:=Right-1;
     end loop;
     if Left =< Right then
       if Left < Right then
         swap(Field(Left), Field(Right));
       end if;
       Left:=Left + 1;
       Right:=Right-1;
     end if;
   end loop;
   if L<Right then local_q_sort(L, Right) end if;
   if R>Left  then Local_Q_Sort(Left, R)  end if;
 end Local_Q_Sort;
begin
 Local_Q_Sort(Field'First, Field'Last);
end Q_Sort;


farvel
  jimmy
--