/*
 * Sort an array of ints using quicksort. 
 */
public static void quicksort(int [] a, int left, int right) 
{
    /* Base case */
    if (left >= right) return;

    /* Select pivot and place it in rightmost location    */
    int pivot = A[right];  /* This selects rightmost as pivot.  POOR CHOICE.  */

    int i=0, j = right-1;

    while (i <= j) {

	/* Advance i to point to a value larger than the pivot */
	while (i < right && a[i] <= pivot)
	    i ++;

	/* Decrement j to point to a value smaller than pivot  */
	while (j >= 0 && a[j] >= pivot)
	    j --;

	/* If pointers have not crossed, swap A[i] and A[j]. */
	if (i < j) {
	    int tmp = A[i];
	    A[i] = A[j];
	    A[j] = tmp;
	}
    }
    /* Swap A[i] with the pivot */
    tmp = A[i];
    A[i] = A[right];
    A[right] = tmp;

    /* Recurse on sub-arrays */
    quicksort (A, left, i-1);
    quicksort (A, i+1, right);
}