// Changes the value of the item stored in the pairing heap.
// pos is any Position returned by insert.
// newVal is the new value, which must be smaller
// than the currently stored value.
// Throws ArgumentException if pos is null.
// Throws IllegalValueException if new value is larger than old.
public void DecreaseKey(IPriorityQueuePosition <AnyType> pos, AnyType newVal)
{
if (pos == null)
{
throw new ArgumentException("null Position passed to decreaseKey");
}
PairNode p = (PairNode)pos;
if (p.element.CompareTo(newVal) < 0)
{
throw new IllegalValueException("newVal/oldval: " + newVal + " /" + p.element);
}
p.element = newVal;
if (p != root)
{
if (p.nextSibling != null)
{
p.nextSibling.prev = p.prev;
}
if (p.prev.leftChild == p)
{
p.prev.leftChild = p.nextSibling;
}
else
{
p.prev.nextSibling = p.nextSibling;
}
p.nextSibling = null;
root = CompareAndLink(root, p);
}
}
// Throws InvalidOperationException because no IPriorityQueuePosition are returned
// by the Insert method for BinaryHeap.
public void DecreaseKey(IPriorityQueuePosition <AnyType> p, AnyType newVal)
{
throw new InvalidOperationException("Cannot use decreaseKey for binary heap");
}
