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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: Quicksort algorithm in ada
Date: Wed, 12 Apr 2006 14:22:37 +0000 (UTC)
Organization: IKS GmbH Jena
Message-ID: <slrne3q39d.3te.lutz@taranis.iks-jena.de>
References: <443d040b$1@news.uni-rostock.de>
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Date: 2006-04-12T14:22:37+00:00
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* Thomas Krueger wrote:
> Do you know the trick or a link to a good Ada implementation of quicksort.

The classic algorithm is easy to implement. You are free to make it generic.

with Ada.Text_IO;
use  Ada.Text_IO;

procedure t is
  procedure qsort(f : in out String) is
    procedure swap(i,j : Positive) is
      t : Character := f(i);
    begin
      f(i) := f(j);
      f(j) := t;
    end swap;

    i : Natural := f'First;
    j : Natural := f'Last;
  begin
    if f'Length > 1 then
      while i<j loop
        while i<j loop
	  if f(i) > f(j) then
	    swap(i,j);
	    j := Positive'Pred(j);
	    exit;
	  end if;
	  i := Positive'Succ(i);
        end loop;
        while i<j loop
	  if f(i) > f(j) then
	    swap(i,j);
	    i := Positive'Succ(i);
	    exit;
	  end if;
	  j := Positive'Pred(j);
  	end loop;
      end loop;
      qsort(f(f'First .. Positive'Pred(j)));
      qsort(f(Positive'Succ(i) .. f'Last));
    end if;
  end qsort;
  
  buff : String(1 .. 80);
  last : Natural;
begin
  Get_Line(buff, last);
  qsort(buff(buff'First .. last));
  Put_Line(buff(buff'First .. last));
end t;