//  File: quicksort4.C
//
//  template "implementation" for Quicksort

#include "ordered.h"
#include "quicksort4.h"


//==========================================================================
// local function prototypes
//

static int partition(Ordered **A, int low, int high) ;

static void RecQuickSort(Ordered **A, int low, int high) ;


//==========================================================================
// function definitions
//

static int partition(Ordered **A, int low, int high) {
   Ordered *x, *temp ;
   int i, j ;

   i = low - 1;
   j = high + 1;
   x = A[low]->clone() ;

   while (true) {

      // Find an element less than x
      do {
         j = j - 1;
      } while (A[j]->cmp(x) > 0) ;

      // Find an element greater than x
      do {
         i = i + 1;
      } while (A[i]->cmp(x) < 0);

      // swap smaller and bigger elements, if needed
      //
      if (i < j) {
         temp = A[j] ;
         A[j] = A[i] ;
         A[i] = temp ;
      } else {
         return j;
      }
    }
}


static void RecQuickSort(Ordered **A, int low, int high) {
   int q ;

   if (low >= high) return ;

   q = partition(A, low, high) ;

   RecQuickSort(A, low, q) ;
   RecQuickSort(A, q + 1, high) ;
}


void QuickSort(Ordered **A, int n) {

   RecQuickSort(A, 0, n-1) ;
}