/** *heapsort */
private static int leftChild(int i)
{
   return 2 * i +1;
}

private static <AnyType extends Comparable<? super AnyType>>
void percDown(AnyType [] a, int i, int n)
{
   int child;
   AnyType tmp;

   for(tmp= a[i]; leftChild(i)< n; i= child)
   {
      child= leftChild(i);
      if(child != n-1 && a[child].compareTo(a[child+1])< 0)
         child++;
      if(tmp.compareTo(a[child])< 0)
         a[i]= a[child];
      else
         break;
   }

   a[i]= tmp;
}
// Standard heapsort
public static <AnyType extends Comparable<? super AnyType>>
void heapsort(AnyType[] a)
{
   for(int i= a.length/2 -1; i>= 0; i--)
      //buildHeap
      perDown(a, i, a.length);

   for(int i= a.length-1; i> 0; i--)
   {
      swapReferences(a, 0, i);

      //deleteMax
      perDown(a, 0, i);
   }

}