problem with quicksort

Question

Possible Duplicate:
what is mistake in this code

i have following code from algorithm in c++

public class improved_quicksort {
    public static final int m=10;
    public static int partition(int a[],int l,int r){
        int i=l-1;
        int j=r;
        int v=a[r];
        while (true){
              while(a[++i]<v);
              while (a[--j]>v)  if (j==i)  break;
                if (i>=j)   break;
              exch(a,i,j);

        }
        exch(a,i,r);

        return i;
    }

    public static void quicksort(int a[],int l,int r){

         if ((r-l)<m)   return;
         exch (a,(l+r)/2,r-1);
          compex(a,l,r-1);
          compex(a,l,r);
          compex(a,r-1,r);

          int i=partition(a,l+1,r-1);
          quicksort(a,l,i-1);
          quicksort(a,i+1,r);
    }

    public static void compex(int a[],int i,int j){

         if (a[i]<a[j]){
             int t=a[i];
             a[i]=a[j];
             a[j]=t;
         }
    }

    public static void main(String[] args) {
      int a[]=new int[]{12,10,23,21,11,34,56,38,50,40,60,76,67};
      quicksort(a,0,a.length-1);
       for (int i=0;i<a.length;i++){
           System.out.println(a[i]);
       }
    }

    public static void exch(int a[],int i,int j){
         int k=a[i];
         a[i]=a[j];
         a[j]=k;
    }
}

but result is:

67
10
11
23
12
34
76
38
50
40
60
56
21

Answer 1

here is a good c++ quicksort page: http://orac.amt.edu.au/wiki/Quicksort

Answer 2

Here is a quicksort routine I wrote some time ago. You may want to look at it as a reference.

public class InPlaceQuickSort {
    public int selectPivot(int[] arr, int low, int high) {
        return arr[low];
    }
    public void sort(int[] arr) {
        sort(arr, 0, arr.length - 1);
    }
    public void sort(int[] arr, int lowbound, int highbound) {
        if (lowbound >= highbound) return;
        int pivot = selectPivot(arr, lowbound, highbound);
        int low = lowbound, high = highbound;
        while (low <= high) {
            if (arr[low] > pivot) {
                swap(arr, low, high--);
            } else if (arr[high] < pivot) {
                swap(arr, low++, high);
            } else {
                low++; high--;
            }
        }
        sort(arr, lowbound, high);
        sort(arr, low, highbound);
    }

    /* swaps arr[a] with arr[b] */
    public void swap(int[] arr, int a, int b) {
        int tmp = arr[a];
        arr[a] = arr[b];
        arr[b] = tmp;
    }
}