/*
 * @(#)QSortAlgorithm.java   1.6f 95/01/31 James Gosling
 *
 * Copyright (c) 1994-1995 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL or COMMERCIAL purposes and
 * without fee is hereby granted. 
 * Please refer to the file http://java.sun.com/copy_trademarks.html
 * for further important copyright and trademark information and to
 * http://java.sun.com/licensing.html for further important licensing
 * information for the Java (tm) Technology.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * THIS SOFTWARE IS NOT DESIGNED OR INTENDED FOR USE OR RESALE AS ON-LINE
 * CONTROL EQUIPMENT IN HAZARDOUS ENVIRONMENTS REQUIRING FAIL-SAFE
 * PERFORMANCE, SUCH AS IN THE OPERATION OF NUCLEAR FACILITIES, AIRCRAFT
 * NAVIGATION OR COMMUNICATION SYSTEMS, AIR TRAFFIC CONTROL, DIRECT LIFE
 * SUPPORT MACHINES, OR WEAPONS SYSTEMS, IN WHICH THE FAILURE OF THE
 * SOFTWARE COULD LEAD DIRECTLY TO DEATH, PERSONAL INJURY, OR SEVERE
 * PHYSICAL OR ENVIRONMENTAL DAMAGE ("HIGH RISK ACTIVITIES").  SUN
 * SPECIFICALLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR
 * HIGH RISK ACTIVITIES.
 */

/** A quick sort demonstration algorithm. <br />
 *  <br />
 *  Author James Gosling, his version 1.6f, 31 Jan 1995<br />
 *  <br />
 *  19 Feb 1996: Fixed to avoid infinite loop discovered by Paul Haeberli.
 *          Misbehaviour expressed when the pivot element was not unique.<br />
 *  <br />
 *  Modif. 15.11.2005, Albrecht Weinert (a-weinert.de) :<br />
 *  {@link SortApplet.SortAlgorithm} + Kleinigkeiten.<br />  
 *  <br />
 *  @author   Albrecht Weinert
 *  @version  V.161, 28.05.2011
 */
public final class QSortAlgorithm extends SortApplet.SortAlgorithm {

   void sort(int[] a, int lo0, int hi0) {
      int lo = lo0;
      int hi = hi0;
      pause(lo, hi);
      if (lo >= hi) {
         return;
      } else if( lo == hi - 1 ) {
         //sort a two element list by swapping if necessary 
         if (a[lo] > a[hi]) {
            int temp = a[lo];
            a[lo] = a[hi];
            a[hi] = temp;
         }
         return;
      }
      
      // Pick a pivot and move it out of the way
      int pivot = a[(lo + hi) / 2];
      a[(lo + hi) / 2] = a[hi];
      a[hi] = pivot;
      
      while (lo < hi) {
         /* Search forward from a[lo] until an element is found that
          *  is greater than the pivot or lo >= hi 
          */
         while (a[lo] <= pivot && lo < hi) {
            ++lo;
         }
         
         /* Search backward from a[hi] until element is found that
          *  is less than the pivot, or lo >= hi
          */
         while (pivot <= a[hi] && lo < hi ) {
            --hi;
         }
         
         //  Swap elements a[lo] and a[hi]
         if( lo < hi ) {
            int temp = a[lo];
            a[lo] = a[hi];
            a[hi] = temp;
            pause();
         }
         
         if (stopRequested)  return; // Abbruch
      }
      
      // Put the median in the "center" of the list
      a[hi0] = a[hi];
      a[hi] = pivot;
      
      /* Recursive calls, elements a[lo0] to a[lo-1] are less than or
       *  equal to pivot, elements a[hi+1] to a[hi0] are greater than
       *  pivot.
       */
      sort(a, lo0, lo-1);
      sort(a, hi+1, hi0);
   }
   
   @Override void sort(int[] a)  {
      sort(a, 0, a.length-1);
   } // sort(int[])
}