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Fibonacci Heaps
Actual Amortized
Insert O(1) O(1)
Remove min (or max) O(n) O(log n)
Meld O(1) O(1)
Remove O(n) O(log n)
Decrease key (or
increase)
O(n) O(1)
Single Source All Destinations
Shortest Paths
Greedy Single Source All Destinations
• Known as Dijkstra’s algorithm.
• Let d(i) be the length of a shortest one edge
extension of an already generated shortest path,
the one edge extension ends at vertex i.
• The next shortest path is to an as yet unreached
vertex for which the d() value is least.
• After the next shortest path is generated, some
d() values are updated (decreased).
Operations On d()
• Remove min.
Done O(n) times, where n is the number of vertices in
the graph.
• Decrease d().
Done O(e) times, where e is the number of edges in
the graph.
• Array.
O(n^2 ) overall complexity.
• Min heap.
O(nlog n + elog n) overall complexity.
• Fibonacci heap.
O(nlog n + e) overall complexity.
Node Structure
• Degree, Child, Data
• Left and Right Sibling
Used for circular doubly linked list of siblings.
• Parent
Pointer to parent node.
• ChildCut
True if node has lost a child since it became a child
of its current parent.
Set to false by remove min, which is the only
operation that makes one node a child of another.
Undefined for a root node.
Fibonacci Heap Representation
• Degree, Parent and ChildCut fields not shown.
A
Remove(theNode)
• theNode points to the Fibonacci heap node
that contains the element that is to be
removed.
• theNode points to min element => do a
remove min.
In this case, complexity is the same as that for
remove min.
Remove(theNode)
• theNode points to an element other than the min
element.
Remove theNode from its doubly linked sibling list.
If sibling list becomes empty, make parent’s child pointer
null.
Set parent field of theNode’s children to null.
Combine top-level list and children list of theNode; do not
pairwise combine equal degree trees.
Free theNode.
• In this case, actual complexity is O(log n) (assuming
theNode has O(log n) children).
Remove(theNode)
DecreaseKey(theNode, theAmount)
If theNode is not a root and new key < parent
key, remove subtree rooted at theNode from its
doubly linked sibling list.
Insert into top-level list.
theNode
DecreaseKey(theNode, theAmount)
Update heap pointer if necessary
Cascading Cut
• When theNode is cut out of its sibling list in a
remove or decrease key operation, follow path
from parent of theNode to the root.
• Encountered nodes (other than root) with
ChildCut = true are cut from their sibling lists
and inserted into top-level list.
• Stop at first node with ChildCut = false.
• For this node, set ChildCut = true.
Cascading Cut Example
T
F
Cascading Cut Example
F 9 8
Cascading Cut Example
T 9 8
Actual complexity of cascading cut is O(h) = O(n).
