/// <summary> Change the value of the item stored in the pairing heap.
/// Does nothing if newVal is larger than the currently stored value.
/// </summary>
/// <param name="p">any node returned by addItem.
/// </param>
/// <param name="newVal">the new value, which must be smaller
/// than the currently stored value.
/// </param>
public virtual void decreaseKey(PairNode p, Comparable newVal)
{
if (p.element.compareTo(newVal) < 0)
{
return; // newVal cannot be bigger
}
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);
}
}
/// <summary> Insert into the priority queue, and return a PairNode
/// that can be used by decreaseKey.
/// Duplicates are allowed.
/// </summary>
/// <param name="x">the item to insert.
/// </param>
/// <returns> the node containing the newly inserted item.
/// </returns>
public virtual PairNode insert(Comparable x)
{
PairNode newNode = new PairNode(x);
if (root == null)
{
root = newNode;
}
else
{
root = compareAndLink(root, newNode);
}
return(newNode);
}
private PairNode[] doubleIfFull(PairNode[] array, int index)
{
if (index == array.Length)
{
PairNode[] oldArray = array;
array = new PairNode[index * 2];
for (int i = 0; i < index; i++)
{
array[i] = oldArray[i];
}
}
return(array);
}
/// <summary> Internal method that implements two-pass merging.</summary>
/// <param name="firstSibling">the root of the conglomerate;
/// assumed not null.
/// </param>
private PairNode combineSiblings(PairNode firstSibling)
{
if (firstSibling.nextSibling == null)
{
return(firstSibling);
}
// Store the subtrees in an array
int numSiblings = 0;
for (; firstSibling != null; numSiblings++)
{
treeArray = doubleIfFull(treeArray, numSiblings);
treeArray[numSiblings] = firstSibling;
firstSibling.prev.nextSibling = null; // break links
firstSibling = firstSibling.nextSibling;
}
treeArray = doubleIfFull(treeArray, numSiblings);
treeArray[numSiblings] = null;
// Combine subtrees two at a time, going left to right
int i = 0;
for (; i + 1 < numSiblings; i += 2)
{
treeArray[i] = compareAndLink(treeArray[i], treeArray[i + 1]);
}
int j = i - 2;
// j has the result of last compareAndLink.
// If an odd number of trees, get the last one.
if (j == numSiblings - 3)
{
treeArray[j] = compareAndLink(treeArray[j], treeArray[j + 2]);
}
// Now go right to left, merging last tree with
// next to last. The result becomes the new last.
for (; j >= 2; j -= 2)
{
treeArray[j - 2] = compareAndLink(treeArray[j - 2], treeArray[j]);
}
return(treeArray[0]);
}
public static void Main(System.String[] args)
{
PairHeap h = new PairHeap();
int numItems = 10000;
int i = 37;
int j;
System.Console.Out.WriteLine("Checking; no bad output is good");
for (i = 37; i != 0; i = (i + 37) % numItems)
{
h.insert(new MyInteger(i));
}
for (i = 1; i < numItems; i++)
{
if (((MyInteger)(h.deleteMin())).intValue() != i)
{
System.Console.Out.WriteLine("Oops! " + i);
}
}
PairNode[] p = new PairNode[numItems];
for (i = 0, j = numItems / 2; i < numItems; i++, j = (j + 71) % numItems)
{
p[j] = h.insert(new MyInteger(j + numItems));
}
for (i = 0, j = numItems / 2; i < numItems; i++, j = (j + 53) % numItems)
{
h.decreaseKey(p[j], new MyInteger(((MyInteger)p[j].element).intValue() - numItems));
}
i = -1;
while (!h.Empty)
{
if (((MyInteger)(h.deleteMin())).intValue() != ++i)
{
System.Console.Out.WriteLine("Oops! " + i + " ");
}
}
System.Console.Out.WriteLine("Check completed");
}
/// <summary> Internal method that is the basic operation to maintain order.
/// Links first and second together to satisfy heap order.
/// </summary>
/// <param name="first">root of tree 1, which may not be null.
/// first.nextSibling MUST be null on entry.
/// </param>
/// <param name="second">root of tree 2, which may be null.
/// </param>
/// <returns> result of the tree merge.
/// </returns>
private PairNode compareAndLink(PairNode first, PairNode second)
{
if (second == null)
{
return(first);
}
if (second.element.compareTo(first.element) < 0)
{
// Attach first as leftmost child of second
second.prev = first.prev;
first.prev = second;
first.nextSibling = second.leftChild;
if (first.nextSibling != null)
{
first.nextSibling.prev = first;
}
second.leftChild = first;
return(second);
}
else
{
// Attach second as leftmost child of first
second.prev = first;
first.nextSibling = second.nextSibling;
if (first.nextSibling != null)
{
first.nextSibling.prev = first;
}
second.nextSibling = first.leftChild;
if (second.nextSibling != null)
{
second.nextSibling.prev = second;
}
first.leftChild = second;
return(first);
}
}
