/**
     * selection sort.
     * @param a an array of Comparable items.
     */
    public static void selectionSort( Comparable [ ] a )
    {
	for (int i = 0; i < a.length-1; i++)
	{
	    int min = i;
	    for (int j = i+1; j < a.length; j++)
		if (a[j].compareTo(a[min]) < 0)
		    min = j;

	    Comparable tmp = a[min];
	    a[min] = a[i];
	    a[i] = tmp;
	}
    }