Data Structures, Algorithms, & Applications in Java
Chapter 19, Exercise 21

public class ModifiedQuickSort
{
   // data member
   static Comparable [] a;   // array of elements to be sorted

   /** sort the elements a[0 : a.length - 1] using the quick sort method */
   public static void quickSort(Comparable [] a)
   {
      ModifiedQuickSort.a = a;
      if (a.length <= 1) return;
      // move largest element to right end
      MyMath.swap(a, a.length - 1, MyMath.max(a, a.length - 1));
      quickSort(0, a.length - 2);
   }
   
   /** sort a[l:r], a[r+1] >= a[l:r] */
   private static void quickSort(int l, int r)
   {
      while (leftEnd < rightEnd)
      {// at least 2 elements to sort
         int leftCursor = leftEnd,        // left-to-right cursor
             rightCursor = rightEnd + 1;  // right-to-left cursor
         Comparable pivot = a[leftEnd];
      
         // swap elements >= pivot on left side
         // with elements <= pivot on right side
         while (true)
         {
            do
            {// find >= element on left side
               leftCursor++;
            } while (a[leftCursor].compareTo(pivot) < 0);
   
            do
            {// find <= element on right side
               rightCursor--;
            } while (a[rightCursor].compareTo(pivot) > 0);
   
            if (leftCursor >= rightCursor) break;  // swap pair not found
            MyMath.swap(a, leftCursor, rightCursor);
         }
      
         // place pivot
         a[leftEnd] = a[rightCursor];
         a[rightCursor] = pivot;
      
         quickSort(leftEnd, rightCursor - 1);   // sort left segment
         leftEnd = rightCursor + 1;             // set to sort right segment
      }
   }
}