Binary Heap Queue
/*
* Copyright 2005 JBoss Inc
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.util.Comparator;
import java.util.NoSuchElementException;
public class BinaryHeapQueue implements Queue, Externalizable {
/** The default capacity for a binary heap. */
private final static int DEFAULT_CAPACITY = 13;
/** The comparator used to order the elements */
private Comparator comparator;
/** The number of elements currently in this heap. */
private int size;
/** The elements in this heap. */
private Queueable[] elements;
public BinaryHeapQueue() {
}
/**
* Constructs a new <code>BinaryHeap</code> that will use the given
* comparator to order its elements.
*
* @param comparator
* the comparator used to order the elements, null means use natural
* order
*/
public BinaryHeapQueue(final Comparator comparator) {
this(comparator, BinaryHeapQueue.DEFAULT_CAPACITY);
}
/**
* Constructs a new <code>BinaryHeap</code>.
*
* @param comparator
* the comparator used to order the elements, null means use natural
* order
* @param capacity
* the initial capacity for the heap
* @throws IllegalArgumentException
* if <code>capacity</code> is <= <code>0</code>
*/
public BinaryHeapQueue(final Comparator comparator, final int capacity) {
if (capacity <= 0) {
throw new IllegalArgumentException("invalid capacity");
}
// +1 as 0 is noop
this.elements = new Queueable[capacity + 1];
this.comparator = comparator;
}
// -----------------------------------------------------------------------
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
comparator = (Comparator) in.readObject();
elements = (Queueable[]) in.readObject();
size = in.readInt();
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject(comparator);
out.writeObject(elements);
out.writeInt(size);
}
/**
* Clears all elements from queue.
*/
public void clear() {
this.elements = new Queueable[this.elements.length]; // for gc
this.size = 0;
}
/**
* Tests if queue is empty.
*
* @return <code>true</code> if queue is empty; <code>false</code>
* otherwise.
*/
public boolean isEmpty() {
return this.size == 0;
}
/**
* Tests if queue is full.
*
* @return <code>true</code> if queue is full; <code>false</code>
* otherwise.
*/
public boolean isFull() {
// +1 as Queueable 0 is noop
return this.elements.length == this.size + 1;
}
/**
* Returns the number of elements in this heap.
*
* @return the number of elements in this heap
*/
public int size() {
return this.size;
}
/**
* Inserts an Queueable into queue.
*
* @param element
* the Queueable to be inserted
*/
public synchronized void enqueue(final Queueable element) {
if (isFull()) {
grow();
}
percolateUpMinHeap(element);
}
/**
* Returns the Queueable on top of heap and remove it.
*
* @return the Queueable at top of heap
* @throws NoSuchElementException
* if <code>isEmpty() == true</code>
*/
public synchronized Queueable dequeue() throws NoSuchElementException {
if (isEmpty()) {
return null;
}
final Queueable result = this.elements[1];
result.dequeue();
// Code bellow was removed because it is already executed
// inside result.dequeue()
//
// setElement(1, this.elements[this.size--]);
// this.elements[this.size + 1] = null;
//
// if (this.size != 0) {
// percolateDownMinHeap(1);
// }
return result;
}
/**
*
* @param index
*/
public synchronized Queueable dequeue(final int index) {
if (index < 1 || index > this.size) {
// throw new NoSuchElementException();
return null;
}
final Queueable result = this.elements[index];
setElement(index, this.elements[this.size]);
this.elements[this.size] = null;
this.size--;
if (this.size != 0 && index <= this.size) {
int compareToParent = 0;
if (index > 1) {
compareToParent = compare(this.elements[index], this.elements[index / 2]);
}
if (index > 1 && compareToParent < 0) {
percolateUpMinHeap(index);
} else {
percolateDownMinHeap(index);
}
}
return result;
}
/**
* Percolates Queueable down heap from the position given by the index. <p/>
* Assumes it is a minimum heap.
*
* @param index
* the index for the Queueable
*/
private void percolateDownMinHeap(final int index) {
final Queueable element = this.elements[index];
int hole = index;
while ((hole * 2) <= this.size) {
int child = hole * 2;
// if we have a right child and that child can not be percolated
// up then move onto other child
if (child != this.size && compare(this.elements[child + 1], this.elements[child]) < 0) {
child++;
}
// if we found resting place of bubble then terminate search
if (compare(this.elements[child], element) >= 0) {
break;
}
setElement(hole, this.elements[child]);
hole = child;
}
setElement(hole, element);
}
/**
* Percolates Queueable up heap from the position given by the index. <p/>
* Assumes it is a minimum heap.
*
* @param index
* the index of the Queueable to be percolated up
*/
private void percolateUpMinHeap(final int index) {
int hole = index;
final Queueable element = this.elements[hole];
while (hole > 1 && compare(element, this.elements[hole / 2]) < 0) {
// save Queueable that is being pushed down
// as the Queueable "bubble" is percolated up
final int next = hole / 2;
setElement(hole, this.elements[next]);
hole = next;
}
setElement(hole, element);
}
/**
* Percolates a new Queueable up heap from the bottom. <p/> Assumes it is a
* minimum heap.
*
* @param element
* the Queueable
*/
private void percolateUpMinHeap(final Queueable element) {
setElement(++this.size, element);
percolateUpMinHeap(this.size);
}
/**
* Compares two objects using the comparator if specified, or the natural
* order otherwise.
*
* @param a
* the first object
* @param b
* the second object
* @return -ve if a less than b, 0 if they are equal, +ve if a greater than b
*/
private int compare(final Queueable a, final Queueable b) {
return this.comparator.compare(a, b);
}
/**
* Increases the size of the heap to support additional elements
*/
private void grow() {
final Queueable[] elements = new Queueable[this.elements.length * 2];
System.arraycopy(this.elements, 0, elements, 0, this.elements.length);
this.elements = elements;
}
/**
*
* @param index
* @param element
*/
private void setElement(final int index, final Queueable element) {
this.elements[index] = element;
element.enqueued(this, index);
}
public Queueable[] getQueueable() {
return this.elements;
}
public Object[] toArray() {
final Object[] result = new Object[this.size];
System.arraycopy(this.elements, 1, result, 0, this.size);
return result;
}
public Object[] toArray(Object a[]) {
if (a.length < this.size) {
a = (Object[]) java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), this.size);
}
System.arraycopy(this.elements, 1, a, 0, this.size);
if (a.length > this.size) {
a[this.size] = null;
}
return a;
}
}
/*
* Copyright 2005 JBoss Inc
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
interface Queue {
public void enqueue(Queueable queueable);
public Queueable dequeue();
public Queueable dequeue(int index);
public boolean isEmpty();
}
/*
* Copyright 2005 JBoss Inc
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
interface Queueable {
public void enqueued(Queue queue, int index);
public void dequeue();
}
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