heap sort

void HeapSort(Comparable[] a)
{
    int n = a.Length;
    for(int k=n/2-1; k>=0; k--)
        sink(a, k, n);
    for(int k=n-1; k>=0; k--)
    {
        exch(a, 0, k);
        sink(a, 0, k-1);
    }
}