/// <summary>
/// Deletes the specified item from this heap.
/// </summary>
/// <param name="item">Item to be deleted.</param>
/// <exception cref="InvalidOperationException">
/// This heap is empty.
/// </exception>
public void Delete(IPriorityQueueItem <T> item)
{
if (this.IsEmpty())
{
throw new InvalidOperationException("This heap is empty.");
}
if (item is FibonacciHeapItem <T> )
{
FibonacciHeapItem <T> fibHeapItem = (FibonacciHeapItem <T>)item;
// Cut the edge joining the containing node x to its parent p.
FibonacciHeapNode <T> x = fibHeapItem.ContainingNode;
if (x.Parent == null)
{
// x is originally a root - just remove it from the list of roots.
if (x == this.minimumNode)
{
this.DeleteMin();
return;
}
else
{
x.LeftSibling.RightSibling = x.RightSibling;
x.RightSibling.LeftSibling = x.LeftSibling;
}
}
else
{
/*
* As x is not a root, remove it from the list of children of
* its parent and decrease its parent's rank.
*/
x.CutEdgeToParent(false, this);
/*
* Form a new list of roots by concatenating the list of children of
* x with the original list of roots.
*/
if (x.SomeChild != null)
{
this.minimumNode.RightSibling.LeftSibling = x.SomeChild.LeftSibling;
x.SomeChild.LeftSibling.RightSibling = this.minimumNode.RightSibling;
this.minimumNode.RightSibling = x.SomeChild;
x.SomeChild.LeftSibling = this.minimumNode;
}
}
this.count--;
}
else
{
throw new ArgumentException("Can work only on Fibonacci Heap items.", "item");
}
}
/// <summary>
/// Inserts the passed item with the specified key into this heap.
/// </summary>
/// <param name="item">Item to insert.</param>
/// <param name="key">Key of the item to insert.</param>
/// <returns>Container that holds the passed item.</returns>
public IPriorityQueueItem <T> Insert(T item, double key)
{
// Contruct a new container for the passed item.
FibonacciHeapItem <T> newItem = new FibonacciHeapItem <T>(item, key);
// Create a new heap consisting of one node containing the passed item.
FibonacciHeap <T> newHeap = new FibonacciHeap <T>();
newHeap.minimumNode = new FibonacciHeapNode <T>(newItem);
newHeap.count = 1;
// Meld this heap and the new one.
this.Meld(newHeap);
return(newItem);
}
/// <summary>
/// Decreases the key of the specified item in this heap by subtracting
/// the passed non-negative real number <c>delta</c>.
/// </summary>
/// <param name="item">Item to decrease the key of.</param>
/// <param name="delta">Non-negative real number to be subtracted from the item's key.</param>
/// <exception cref="ArgumentOutOfRangeException">
/// <c>delta</c> is negative.
/// </exception>
/// <exception cref="InvalidOperationException">
/// This heap is empty.
/// </exception>
public void DecreaseKey(IPriorityQueueItem <T> item, double delta)
{
if (delta < 0)
{
throw new ArgumentOutOfRangeException("delta", "delta has to be non-negative.");
}
if (this.IsEmpty())
{
throw new InvalidOperationException("This heap is empty.");
}
if (item is FibonacciHeapItem <T> )
{
FibonacciHeapItem <T> fibHeapItem = (FibonacciHeapItem <T>)item;
// Subtract delta from the key of the passed item.
fibHeapItem.Key -= delta;
// Cut the edge joining the containing node x to its parent p.
FibonacciHeapNode <T> x = fibHeapItem.ContainingNode;
if (x.Parent != null)
{
/*
* If x is not a root, remove it from the list of children of
* its parent, decrease its parent's rank, and add it to the list
* of roots of this heap in order to preserve the heap order.
*/
x.CutEdgeToParent(true, this);
}
// Redefine the minimum node of this heap, if necessary.
if (fibHeapItem.Key < this.minimumNode.Item.Key)
{
this.minimumNode = x;
}
}
else
{
throw new ArgumentException("Can only work on Fibonacci Heap items.", "item");
}
}
/// <summary>
/// Deletes the item with the minimum key in this heap and returns it.
/// </summary>
/// <returns>Item with the minimum key in this heap.</returns>
/// <exception cref="InvalidOperationException">
/// This heap is empty.
/// </exception>
public IPriorityQueueItem <T> DeleteMin()
{
if (this.IsEmpty())
{
throw new InvalidOperationException("This heap is empty.");
}
/*
* Remove the minimum node x from this heap and concatenate the list of
* children of x with the list of roots of this heap other than x.
*/
FibonacciHeapNode <T> x = this.minimumNode;
FibonacciHeapItem <T> minimumItem = x.Item;
this.count--;
// Remember some node to start with the linking step later on.
FibonacciHeapNode <T> someListNode;
if (x.RightSibling == x)
{
if (x.SomeChild == null)
{
// The heap consists of only the root node.
this.minimumNode = null;
return(minimumItem);
}
else
{
// Root has no siblings - apply linking step to list of children.
someListNode = x.SomeChild;
}
}
else
{
if (x.SomeChild == null)
{
// Root has no children - apply linking step to list of siblings.
x.LeftSibling.RightSibling = x.RightSibling;
x.RightSibling.LeftSibling = x.LeftSibling;
someListNode = x.LeftSibling;
}
else
{
// Concatenate children and siblings and apply linking step.
x.LeftSibling.RightSibling = x.SomeChild;
x.SomeChild.LeftSibling.RightSibling = x.RightSibling;
x.RightSibling.LeftSibling = x.SomeChild.LeftSibling;
x.SomeChild.LeftSibling = x.LeftSibling;
someListNode = x.SomeChild;
}
}
// Linking Step.
/*
* Create an hashtable indexed by rank, from one up to the maximum
* possible rank, each entry pointing to a tree root.
*/
Dictionary <int, FibonacciHeapNode <T> > rankIndexedRoots = new Dictionary <int, FibonacciHeapNode <T> >();
// Insert the roots one-by-one into the appropriate table positions.
FibonacciHeapNode <T> nextOldRoot = someListNode;
do
{
FibonacciHeapNode <T> shouldBeInserted = nextOldRoot;
nextOldRoot = nextOldRoot.RightSibling;
while (shouldBeInserted != null)
{
/*
* If the position is already occupied, perform a linking
* step and attempt to insert the root of the new tree into
* the next higher position.
*/
if (rankIndexedRoots.ContainsKey(shouldBeInserted.Rank))
{
FibonacciHeapNode <T> other = rankIndexedRoots[shouldBeInserted.Rank];
rankIndexedRoots.Remove(shouldBeInserted.Rank);
shouldBeInserted = shouldBeInserted.Link(other);
}
else
{
rankIndexedRoots.Add(shouldBeInserted.Rank, shouldBeInserted);
shouldBeInserted = null;
}
}
}while (nextOldRoot != someListNode);
/*
* Form a list of the remaining roots, in the process finding a root
* containing an item of minimum key to serve as the minimum node of the
* modified heap.
*/
List <FibonacciHeapNode <T> > newRoots = rankIndexedRoots.Values.ToList();
// Start with the first new root.
FibonacciHeapNode <T> firstNewRoot = newRoots[0];
this.minimumNode = firstNewRoot;
this.minimumNode.Parent = null;
FibonacciHeapNode <T> currentNewRoot = firstNewRoot;
for (int i = 1; i < newRoots.Count; i++)
{
// Get the next new root.
FibonacciHeapNode <T> previousNewRoot = currentNewRoot;
currentNewRoot = newRoots[i];
// Update pointers.
previousNewRoot.RightSibling = currentNewRoot;
currentNewRoot.LeftSibling = previousNewRoot;
currentNewRoot.Parent = null;
// Check for new minimum node.
if (currentNewRoot.Item.Key < this.minimumNode.Item.Key)
{
this.minimumNode = currentNewRoot;
}
}
currentNewRoot.RightSibling = firstNewRoot;
firstNewRoot.LeftSibling = currentNewRoot;
return(minimumItem);
}
