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The Commons Collections BinaryHeap.java source code
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.commons.collections;
import java.util.AbstractCollection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Binary heap implementation of <code>PriorityQueue.
* <p>
* The <code>PriorityQueue interface has now been replaced for most uses
* by the <code>Buffer interface. This class and the interface are
* retained for backwards compatibility. The intended replacement is
* {@link org.apache.commons.collections.buffer.PriorityBuffer PriorityBuffer}.
* <p>
* The removal order of a binary heap is based on either the natural sort
* order of its elements or a specified {@link Comparator}. The
* {@link #pop()} method always returns the first element as determined
* by the sort order. (The <code>isMinHeap flag in the constructors
* can be used to reverse the sort order, in which case {@link #pop()}
* will always remove the last element.) The removal order is
* <i>not the same as the order of iteration; elements are
* returned by the iterator in no particular order.
* <p>
* The {@link #insert(Object)} and {@link #pop()} operations perform
* in logarithmic time. The {@link #peek()} operation performs in constant
* time. All other operations perform in linear time or worse.
* <p>
* Note that this implementation is not synchronized. Use SynchronizedPriorityQueue
* to provide synchronized access to a <code>BinaryHeap:
*
* <pre>
* PriorityQueue heap = new SynchronizedPriorityQueue(new BinaryHeap());
* </pre>
*
* @deprecated Replaced by PriorityBuffer in buffer subpackage.
* Due to be removed in v4.0.
* @since Commons Collections 1.0
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*
* @author Peter Donald
* @author Ram Chidambaram
* @author Michael A. Smith
* @author Paul Jack
* @author Stephen Colebourne
*/
public final class BinaryHeap extends AbstractCollection
implements PriorityQueue, Buffer {
/**
* The default capacity for a binary heap.
*/
private final static int DEFAULT_CAPACITY = 13;
/**
* The number of elements currently in this heap.
*/
int m_size; // package scoped for testing
/**
* The elements in this heap.
*/
Object[] m_elements; // package scoped for testing
/**
* If true, the first element as determined by the sort order will
* be returned. If false, the last element as determined by the
* sort order will be returned.
*/
boolean m_isMinHeap; // package scoped for testing
/**
* The comparator used to order the elements
*/
Comparator m_comparator; // package scoped for testing
/**
* Constructs a new minimum binary heap.
*/
public BinaryHeap() {
this(DEFAULT_CAPACITY, true);
}
/**
* Constructs a new <code>BinaryHeap 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 BinaryHeap(Comparator comparator) {
this();
m_comparator = comparator;
}
/**
* Constructs a new minimum binary heap with the specified initial capacity.
*
* @param capacity The initial capacity for the heap. This value must
* be greater than zero.
* @throws IllegalArgumentException
* if <code>capacity is <= 0
*/
public BinaryHeap(int capacity) {
this(capacity, true);
}
/**
* Constructs a new <code>BinaryHeap.
*
* @param capacity the initial capacity for the heap
* @param comparator the comparator used to order the elements, null
* means use natural order
* @throws IllegalArgumentException
* if <code>capacity is <= 0
*/
public BinaryHeap(int capacity, Comparator comparator) {
this(capacity);
m_comparator = comparator;
}
/**
* Constructs a new minimum or maximum binary heap
*
* @param isMinHeap if <code>true the heap is created as a
* minimum heap; otherwise, the heap is created as a maximum heap
*/
public BinaryHeap(boolean isMinHeap) {
this(DEFAULT_CAPACITY, isMinHeap);
}
/**
* Constructs a new <code>BinaryHeap.
*
* @param isMinHeap true to use the order imposed by the given
* comparator; false to reverse that order
* @param comparator the comparator used to order the elements, null
* means use natural order
*/
public BinaryHeap(boolean isMinHeap, Comparator comparator) {
this(isMinHeap);
m_comparator = comparator;
}
/**
* Constructs a new minimum or maximum binary heap with the specified
* initial capacity.
*
* @param capacity the initial capacity for the heap. This value must
* be greater than zero.
* @param isMinHeap if <code>true the heap is created as a
* minimum heap; otherwise, the heap is created as a maximum heap.
* @throws IllegalArgumentException
* if <code>capacity is <= 0
*/
public BinaryHeap(int capacity, boolean isMinHeap) {
if (capacity <= 0) {
throw new IllegalArgumentException("invalid capacity");
}
m_isMinHeap = isMinHeap;
//+1 as 0 is noop
m_elements = new Object[capacity + 1];
}
/**
* Constructs a new <code>BinaryHeap.
*
* @param capacity the initial capacity for the heap
* @param isMinHeap true to use the order imposed by the given
* comparator; false to reverse that order
* @param comparator the comparator used to order the elements, null
* means use natural order
* @throws IllegalArgumentException
* if <code>capacity is <= 0
*/
public BinaryHeap(int capacity, boolean isMinHeap, Comparator comparator) {
this(capacity, isMinHeap);
m_comparator = comparator;
}
//-----------------------------------------------------------------------
/**
* Clears all elements from queue.
*/
public void clear() {
m_elements = new Object[m_elements.length]; // for gc
m_size = 0;
}
/**
* Tests if queue is empty.
*
* @return <code>true if queue is empty; false
* otherwise.
*/
public boolean isEmpty() {
return m_size == 0;
}
/**
* Tests if queue is full.
*
* @return <code>true if queue is full; false
* otherwise.
*/
public boolean isFull() {
//+1 as element 0 is noop
return m_elements.length == m_size + 1;
}
/**
* Inserts an element into queue.
*
* @param element the element to be inserted
*/
public void insert(Object element) {
if (isFull()) {
grow();
}
//percolate element to it's place in tree
if (m_isMinHeap) {
percolateUpMinHeap(element);
} else {
percolateUpMaxHeap(element);
}
}
/**
* Returns the element on top of heap but don't remove it.
*
* @return the element at top of heap
* @throws NoSuchElementException if <code>isEmpty() == true
*/
public Object peek() throws NoSuchElementException {
if (isEmpty()) {
throw new NoSuchElementException();
} else {
return m_elements[1];
}
}
/**
* Returns the element on top of heap and remove it.
*
* @return the element at top of heap
* @throws NoSuchElementException if <code>isEmpty() == true
*/
public Object pop() throws NoSuchElementException {
final Object result = peek();
m_elements[1] = m_elements[m_size--];
// set the unused element to 'null' so that the garbage collector
// can free the object if not used anywhere else.(remove reference)
m_elements[m_size + 1] = null;
if (m_size != 0) {
// percolate top element to it's place in tree
if (m_isMinHeap) {
percolateDownMinHeap(1);
} else {
percolateDownMaxHeap(1);
}
}
return result;
}
/**
* Percolates element down heap from the position given by the index.
* <p>
* Assumes it is a minimum heap.
*
* @param index the index for the element
*/
protected void percolateDownMinHeap(final int index) {
final Object element = m_elements[index];
int hole = index;
while ((hole * 2) <= m_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 != m_size && compare(m_elements[child + 1], m_elements[child]) < 0) {
child++;
}
// if we found resting place of bubble then terminate search
if (compare(m_elements[child], element) >= 0) {
break;
}
m_elements[hole] = m_elements[child];
hole = child;
}
m_elements[hole] = element;
}
/**
* Percolates element down heap from the position given by the index.
* <p>
* Assumes it is a maximum heap.
*
* @param index the index of the element
*/
protected void percolateDownMaxHeap(final int index) {
final Object element = m_elements[index];
int hole = index;
while ((hole * 2) <= m_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 != m_size && compare(m_elements[child + 1], m_elements[child]) > 0) {
child++;
}
// if we found resting place of bubble then terminate search
if (compare(m_elements[child], element) <= 0) {
break;
}
m_elements[hole] = m_elements[child];
hole = child;
}
m_elements[hole] = element;
}
/**
* Percolates element up heap from the position given by the index.
* <p>
* Assumes it is a minimum heap.
*
* @param index the index of the element to be percolated up
*/
protected void percolateUpMinHeap(final int index) {
int hole = index;
Object element = m_elements[hole];
while (hole > 1 && compare(element, m_elements[hole / 2]) < 0) {
// save element that is being pushed down
// as the element "bubble" is percolated up
final int next = hole / 2;
m_elements[hole] = m_elements[next];
hole = next;
}
m_elements[hole] = element;
}
/**
* Percolates a new element up heap from the bottom.
* <p>
* Assumes it is a minimum heap.
*
* @param element the element
*/
protected void percolateUpMinHeap(final Object element) {
m_elements[++m_size] = element;
percolateUpMinHeap(m_size);
}
/**
* Percolates element up heap from from the position given by the index.
* <p>
* Assume it is a maximum heap.
*
* @param index the index of the element to be percolated up
*/
protected void percolateUpMaxHeap(final int index) {
int hole = index;
Object element = m_elements[hole];
while (hole > 1 && compare(element, m_elements[hole / 2]) > 0) {
// save element that is being pushed down
// as the element "bubble" is percolated up
final int next = hole / 2;
m_elements[hole] = m_elements[next];
hole = next;
}
m_elements[hole] = element;
}
/**
* Percolates a new element up heap from the bottom.
* <p>
* Assume it is a maximum heap.
*
* @param element the element
*/
protected void percolateUpMaxHeap(final Object element) {
m_elements[++m_size] = element;
percolateUpMaxHeap(m_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(Object a, Object b) {
if (m_comparator != null) {
return m_comparator.compare(a, b);
} else {
return ((Comparable) a).compareTo(b);
}
}
/**
* Increases the size of the heap to support additional elements
*/
protected void grow() {
final Object[] elements = new Object[m_elements.length * 2];
System.arraycopy(m_elements, 0, elements, 0, m_elements.length);
m_elements = elements;
}
/**
* Returns a string representation of this heap. The returned string
* is similar to those produced by standard JDK collections.
*
* @return a string representation of this heap
*/
public String toString() {
final StringBuffer sb = new StringBuffer();
sb.append("[ ");
for (int i = 1; i < m_size + 1; i++) {
if (i != 1) {
sb.append(", ");
}
sb.append(m_elements[i]);
}
sb.append(" ]");
return sb.toString();
}
/**
* Returns an iterator over this heap's elements.
*
* @return an iterator over this heap's elements
*/
public Iterator iterator() {
return new Iterator() {
private int index = 1;
private int lastReturnedIndex = -1;
public boolean hasNext() {
return index <= m_size;
}
public Object next() {
if (!hasNext()) throw new NoSuchElementException();
lastReturnedIndex = index;
index++;
return m_elements[lastReturnedIndex];
}
public void remove() {
if (lastReturnedIndex == -1) {
throw new IllegalStateException();
}
m_elements[ lastReturnedIndex ] = m_elements[ m_size ];
m_elements[ m_size ] = null;
m_size--;
if( m_size != 0 && lastReturnedIndex <= m_size) {
int compareToParent = 0;
if (lastReturnedIndex > 1) {
compareToParent = compare(m_elements[lastReturnedIndex],
m_elements[lastReturnedIndex / 2]);
}
if (m_isMinHeap) {
if (lastReturnedIndex > 1 && compareToParent < 0) {
percolateUpMinHeap(lastReturnedIndex);
} else {
percolateDownMinHeap(lastReturnedIndex);
}
} else { // max heap
if (lastReturnedIndex > 1 && compareToParent > 0) {
percolateUpMaxHeap(lastReturnedIndex);
} else {
percolateDownMaxHeap(lastReturnedIndex);
}
}
}
index--;
lastReturnedIndex = -1;
}
};
}
/**
* Adds an object to this heap. Same as {@link #insert(Object)}.
*
* @param object the object to add
* @return true, always
*/
public boolean add(Object object) {
insert(object);
return true;
}
/**
* Returns the priority element. Same as {@link #peek()}.
*
* @return the priority element
* @throws BufferUnderflowException if this heap is empty
*/
public Object get() {
try {
return peek();
} catch (NoSuchElementException e) {
throw new BufferUnderflowException();
}
}
/**
* Removes the priority element. Same as {@link #pop()}.
*
* @return the removed priority element
* @throws BufferUnderflowException if this heap is empty
*/
public Object remove() {
try {
return pop();
} catch (NoSuchElementException e) {
throw new BufferUnderflowException();
}
}
/**
* Returns the number of elements in this heap.
*
* @return the number of elements in this heap
*/
public int size() {
return m_size;
}
}
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