structure
Class SkewHeap

java.lang.Object
  |
  +--structure.SkewHeap

All Implemented Interfaces:

MergeableHeap, PriorityQueue

public class SkewHeap

extends Object

implements PriorityQueue, MergeableHeap

An implementation of a priority queue using skew heaps. Skew heaps allow one to construct heaps dynamically without explictly balancing the heaps. Main operation is a merge. Most operations execute in amortized logarithmic time, but individual operations may take linear time to execute in the worst case.

Example usage:

To print out a list of programmers sorted by age we could use the following:

 public static void main(String[] argv){
	//initialize a new fib heap
	SkewHeap programmers = new SkewHeap();

	//add programmers and their ages to heap
	//ages current of 7/22/2002
	//add programmers and their ages to heap
	//ages current of 7/22/2002
        programmers.add(new ComparableAssociation(new Integer(22), "Evan"));
	programmers.add(new ComparableAssociation(new Integer(19), "Chris"));
	programmers.add(new ComparableAssociation(new Integer(20), "Shimon"));
	programmers.add(new ComparableAssociation(new Integer(21), "Diane"));
	programmers.add(new ComparableAssociation(new Integer(21), "Lida"));	
	programmers.add(new ComparableAssociation(new Integer(20), "Rob"));	
	programmers.add(new ComparableAssociation(new Integer(20), "Sean"));	

	//print out programmers 
	while(!programmers.isEmpty()){
	    ComparableAssociation p = (ComparableAssociation)programmers.remove();
	    System.out.println(p.getValue() + " is " + p.getKey() + " years old.");
	}
 }
 

Field Summary

protected int	count The number of nodes within heap.
protected BinaryTree	root The root of the skew heap.

Constructor Summary

SkewHeap()
Constructs an empty priority queue.

Method Summary

void	add(Comparable value) Add a value to the priority queue.
void	clear() Remove all the elements from the queue.
Comparable	getFirst() Fetch lowest valued (highest priority) item from queue.
boolean	isEmpty() Determine if the queue is empty.
static void	main(String[] argv)
protected static BinaryTree	merge(BinaryTree left, BinaryTree right)
void	merge(MergeableHeap otherHeap) Merge this heap with another
Comparable	remove() Returns the minimum value from the queue.
int	size() Determine the size of the queue.
String	toString() Construct a string representation of the heap.

Methods inherited from class java.lang.Object

, clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, wait, wait, wait

Field Detail

root

protected BinaryTree root

The root of the skew heap.

count

protected int count

The number of nodes within heap.

Constructor Detail

SkewHeap

public SkewHeap()

Constructs an empty priority queue.

Method Detail

getFirst

public Comparable getFirst()

Fetch lowest valued (highest priority) item from queue.

Specified by:

getFirst in interface PriorityQueue

Precondition:

!isEmpty()

Postcondition:

returns the minimum value in priority queue

Returns:

The smallest value from queue.

remove

public Comparable remove()

Returns the minimum value from the queue.

Specified by:

remove in interface PriorityQueue

Precondition:

!isEmpty()

Postcondition:

returns and removes minimum value from queue

Returns:

The minimum value in the queue.

add

public void add(Comparable value)

Add a value to the priority queue.

Specified by:

add in interface PriorityQueue

Parameters:

value - The value to be added.

Precondition:

value is non-null comparable

Postcondition:

value is added to priority queue

size

public int size()

Determine the size of the queue.

Specified by:

size in interface PriorityQueue

Postcondition:

returns number of elements within queue

Returns:

The number of elements within the queue.

clear

public void clear()

Remove all the elements from the queue.

Specified by:

clear in interface PriorityQueue

Postcondition:

removes all elements from queue

isEmpty

public boolean isEmpty()

Determine if the queue is empty.

Specified by:

isEmpty in interface PriorityQueue

Postcondition:

returns true iff no elements are in queue

Returns:

True if the queue is empty.

merge

public void merge(MergeableHeap otherHeap)

Merge this heap with another

Specified by:

merge in interface MergeableHeap

Parameters:

otherHeap - Heap to be merged with this heap, otherHeap is destroyed by this operation;

Postcondition:

the two heaps are merged and otherHeap is destroyed

merge

protected static BinaryTree merge(BinaryTree left,
                                  BinaryTree right)

toString

public String toString()

Construct a string representation of the heap.

Overrides:

toString in class Object

Postcondition:

returns string representation of heap

Returns:

The string representing the heap.

main

public static void main(String[] argv)