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package java.util; |
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/* |
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* %W% %E% |
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* |
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* Copyright 2003 Sun Microsystems, Inc. All rights reserved. |
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* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. |
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*/ |
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|
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package java.util; |
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/** |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* This queue orders |
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* elements according to an order specified at construction time, which is |
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* specified in the same manner as {@link java.util.TreeSet} and |
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* {@link java.util.TreeMap}: elements are ordered |
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* either according to their <i>natural order</i> (see {@link Comparable}), or |
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* according to a {@link java.util.Comparator}, depending on which |
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* constructor is used. |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* This queue orders elements according to an order specified at construction |
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* time, which is specified in the same manner as {@link java.util.TreeSet} |
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* and {@link java.util.TreeMap}: elements are ordered either according to |
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* their <i>natural order</i> (see {@link Comparable}), or according to a |
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* {@link java.util.Comparator}, depending on which constructor is used. |
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* |
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* <p>The <em>head</em> of this queue is the <em>least</em> element with |
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* respect to the specified ordering. |
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* If multiple elements are tied for least value, the |
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* head is one of those elements. A priority queue does not permit |
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* <tt>null</tt> elements. |
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* respect to the specified ordering. If multiple elements are tied for least |
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* value, the head is one of those elements. A priority queue does not permit |
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* <tt>null</tt> elements. |
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* |
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* <p>The {@link #remove()} and {@link #poll()} methods remove and |
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* return the head of the queue. |
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* <p>The {@link #element()} and {@link #peek()} methods return, but do |
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* not delete, the head of the queue. |
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* |
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* <p>A priority queue has a <i>capacity</i>. The capacity is the |
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* size of the array used internally to store the elements on the |
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* queue. |
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* It is always at least as large as the queue size. As |
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* elements are added to a priority queue, its capacity grows |
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* automatically. The details of the growth policy are not specified. |
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* <p>A priority queue is unbounded, but has a <i>capacity</i>. The |
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* capacity is the size of the array used internally to store the |
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* elements on the queue. It is always at least as large as the queue |
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* size. As elements are added to a priority queue, its capacity |
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* grows automatically. The details of the growth policy are not |
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* specified. |
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* |
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* <p>The Iterator provided in method {@link #iterator()} is <em>not</em> |
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* guaranteed to traverse the elements of the PriorityQueue in any |
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* Multiple threads should not access a <tt>PriorityQueue</tt> |
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* instance concurrently if any of the threads modifies the list |
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* structurally. Instead, use the thread-safe {@link |
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* java.util.concurrent.BlockingPriorityQueue} class. |
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* java.util.concurrent.PriorityBlockingQueue} class. |
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* |
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* |
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* <p>Implementation note: this implementation provides O(log(n)) time |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
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* Java Collections Framework</a>. |
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* @since 1.5 |
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* @version %I%, %G% |
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* @author Josh Bloch |
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*/ |
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public class PriorityQueue<E> extends AbstractQueue<E> |
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/** |
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* Initially fill elements of the queue array under the |
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* knowledge that it is sorted or is another PQ, in which |
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* case we can just place the elements without fixups. |
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* case we can just place the elements in the order presented. |
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*/ |
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private void fillFromSorted(Collection<? extends E> c) { |
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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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queue[++size] = i.next(); |
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} |
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/** |
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* Initially fill elements of the queue array that is |
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* not to our knowledge sorted, so we must add them |
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* one by one. |
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* Initially fill elements of the queue array that is not to our knowledge |
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* sorted, so we must rearrange the elements to guarantee the heap |
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* invariant. |
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*/ |
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private void fillFromUnsorted(Collection<? extends E> c) { |
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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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add(i.next()); |
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queue[++size] = i.next(); |
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heapify(); |
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} |
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/** |
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queue = newQueue; |
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} |
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|
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// Queue Methods |
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|
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|
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/** |
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* Add the specified element to this priority queue. |
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* Inserts the specified element to this priority queue. |
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* |
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* @return <tt>true</tt> |
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* @throws ClassCastException if the specified element cannot be compared |
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return true; |
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} |
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public E poll() { |
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public E peek() { |
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if (size == 0) |
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return null; |
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return (E) remove(1); |
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} |
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|
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public E peek() { |
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return (E) queue[1]; |
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} |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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* |
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* @throws NullPointerException {@inheritDoc} |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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* <p> |
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* This implementation iterates over the specified collection, and adds |
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* each object returned by the iterator to this collection, in turn. |
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* @throws NullPointerException {@inheritDoc} |
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* @param c collection whose elements are to be added to this queue |
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* @return <tt>true</tt> if this queue changed as a result of the |
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* call. |
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* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt> |
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* is <tt>null</tt> |
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* @throws ClassCastException if any element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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return super.addAll(c); |
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} |
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|
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|
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/** |
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* Removes a single instance of the specified element from this |
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* queue, if it is present. More formally, |
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* removes an element <tt>e</tt> such that <tt>(o==null ? e==null : |
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* o.equals(e))</tt>, if the queue contains one or more such |
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* elements. Returns <tt>true</tt> if the queue contained the |
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* specified element (or equivalently, if the queue changed as a |
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* result of the call). |
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* |
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* <p>This implementation iterates over the queue looking for the |
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* specified element. If it finds the element, it removes the element |
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* from the queue using the iterator's remove method.<p> |
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* |
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*/ |
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public boolean remove(Object o) { |
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if (o == null) |
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return false; |
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if (comparator == null) { |
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for (int i = 1; i <= size; i++) { |
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if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) { |
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remove(i); |
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removeAt(i); |
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return true; |
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} |
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} |
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} else { |
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for (int i = 1; i <= size; i++) { |
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if (comparator.compare((E)queue[i], (E)o) == 0) { |
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remove(i); |
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removeAt(i); |
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return true; |
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} |
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} |
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} |
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|
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private class Itr implements Iterator<E> { |
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|
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/** |
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* Index (into queue array) of element to be returned by |
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* subsequent call to next. |
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private int cursor = 1; |
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|
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/** |
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* Index of element returned by most recent call to next or |
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* previous. Reset to 0 if this element is deleted by a call |
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* to remove. |
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* Index of element returned by most recent call to next, |
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* unless that element came from the forgetMeNot list. |
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* Reset to 0 if element is deleted by a call to remove. |
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*/ |
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private int lastRet = 0; |
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|
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*/ |
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private int expectedModCount = modCount; |
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|
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/** |
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* A list of elements that were moved from the unvisited portion of |
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* the heap into the visited portion as a result of "unlucky" element |
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* removals during the iteration. (Unlucky element removals are those |
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* that require a fixup instead of a fixdown.) We must visit all of |
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* the elements in this list to complete the iteration. We do this |
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* after we've completed the "normal" iteration. |
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* |
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* We expect that most iterations, even those involving removals, |
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* will not use need to store elements in this field. |
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*/ |
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private ArrayList<E> forgetMeNot = null; |
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|
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/** |
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* Element returned by the most recent call to next iff that |
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* element was drawn from the forgetMeNot list. |
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*/ |
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private Object lastRetElt = null; |
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|
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public boolean hasNext() { |
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return cursor <= size; |
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return cursor <= size || forgetMeNot != null; |
425 |
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} |
426 |
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|
427 |
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public E next() { |
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checkForComodification(); |
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if (cursor > size) |
429 |
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E result; |
430 |
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if (cursor <= size) { |
431 |
> |
result = (E) queue[cursor]; |
432 |
> |
lastRet = cursor++; |
433 |
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} |
434 |
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else if (forgetMeNot == null) |
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throw new NoSuchElementException(); |
436 |
< |
E result = (E) queue[cursor]; |
437 |
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lastRet = cursor++; |
436 |
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else { |
437 |
> |
int remaining = forgetMeNot.size(); |
438 |
> |
result = forgetMeNot.remove(remaining - 1); |
439 |
> |
if (remaining == 1) |
440 |
> |
forgetMeNot = null; |
441 |
> |
lastRet = 0; |
442 |
> |
lastRetElt = result; |
443 |
> |
} |
444 |
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return result; |
445 |
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} |
446 |
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|
447 |
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public void remove() { |
429 |
– |
if (lastRet == 0) |
430 |
– |
throw new IllegalStateException(); |
448 |
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checkForComodification(); |
449 |
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|
450 |
< |
PriorityQueue.this.remove(lastRet); |
451 |
< |
if (lastRet < cursor) |
452 |
< |
cursor--; |
453 |
< |
lastRet = 0; |
450 |
> |
if (lastRet != 0) { |
451 |
> |
E moved = PriorityQueue.this.removeAt(lastRet); |
452 |
> |
lastRet = 0; |
453 |
> |
if (moved == null) { |
454 |
> |
cursor--; |
455 |
> |
} else { |
456 |
> |
if (forgetMeNot == null) |
457 |
> |
forgetMeNot = new ArrayList<E>(); |
458 |
> |
forgetMeNot.add(moved); |
459 |
> |
} |
460 |
> |
} else if (lastRetElt != null) { |
461 |
> |
PriorityQueue.this.remove(lastRetElt); |
462 |
> |
lastRetElt = null; |
463 |
> |
} else { |
464 |
> |
throw new IllegalStateException(); |
465 |
> |
} |
466 |
> |
|
467 |
|
expectedModCount = modCount; |
468 |
|
} |
469 |
|
|
490 |
|
size = 0; |
491 |
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} |
492 |
|
|
493 |
+ |
public E poll() { |
494 |
+ |
if (size == 0) |
495 |
+ |
return null; |
496 |
+ |
modCount++; |
497 |
+ |
|
498 |
+ |
E result = (E) queue[1]; |
499 |
+ |
queue[1] = queue[size]; |
500 |
+ |
queue[size--] = null; // Drop extra ref to prevent memory leak |
501 |
+ |
if (size > 1) |
502 |
+ |
fixDown(1); |
503 |
+ |
|
504 |
+ |
return result; |
505 |
+ |
} |
506 |
+ |
|
507 |
|
/** |
508 |
< |
* Removes and returns the ith element from queue. Recall |
509 |
< |
* that queue is one-based, so 1 <= i <= size. |
508 |
> |
* Removes and returns the ith element from queue. (Recall that queue |
509 |
> |
* is one-based, so 1 <= i <= size.) |
510 |
|
* |
511 |
< |
* XXX: Could further special-case i==size, but is it worth it? |
512 |
< |
* XXX: Could special-case i==0, but is it worth it? |
511 |
> |
* Normally this method leaves the elements at positions from 1 up to i-1, |
512 |
> |
* inclusive, untouched. Under these circumstances, it returns null. |
513 |
> |
* Occasionally, in order to maintain the heap invariant, it must move |
514 |
> |
* the last element of the list to some index in the range [2, i-1], |
515 |
> |
* and move the element previously at position (i/2) to position i. |
516 |
> |
* Under these circumstances, this method returns the element that was |
517 |
> |
* previously at the end of the list and is now at some position between |
518 |
> |
* 2 and i-1 inclusive. |
519 |
|
*/ |
520 |
< |
private E remove(int i) { |
521 |
< |
assert i <= size; |
520 |
> |
private E removeAt(int i) { |
521 |
> |
assert i > 0 && i <= size; |
522 |
|
modCount++; |
523 |
|
|
524 |
< |
E result = (E) queue[i]; |
525 |
< |
queue[i] = queue[size]; |
524 |
> |
E moved = (E) queue[size]; |
525 |
> |
queue[i] = moved; |
526 |
|
queue[size--] = null; // Drop extra ref to prevent memory leak |
527 |
< |
if (i <= size) |
527 |
> |
if (i <= size) { |
528 |
|
fixDown(i); |
529 |
< |
return result; |
529 |
> |
if (queue[i] == moved) { |
530 |
> |
fixUp(i); |
531 |
> |
if (queue[i] != moved) |
532 |
> |
return moved; |
533 |
> |
} |
534 |
> |
} |
535 |
> |
return null; |
536 |
|
} |
537 |
|
|
538 |
|
/** |
555 |
|
} |
556 |
|
} else { |
557 |
|
while (k > 1) { |
558 |
< |
int j = k >> 1; |
558 |
> |
int j = k >>> 1; |
559 |
|
if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) |
560 |
|
break; |
561 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
576 |
|
private void fixDown(int k) { |
577 |
|
int j; |
578 |
|
if (comparator == null) { |
579 |
< |
while ((j = k << 1) <= size) { |
580 |
< |
if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
579 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
580 |
> |
if (j<size && |
581 |
> |
((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
582 |
|
j++; // j indexes smallest kid |
583 |
+ |
|
584 |
|
if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0) |
585 |
|
break; |
586 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
587 |
|
k = j; |
588 |
|
} |
589 |
|
} else { |
590 |
< |
while ((j = k << 1) <= size) { |
591 |
< |
if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
590 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
591 |
> |
if (j<size && |
592 |
> |
comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
593 |
|
j++; // j indexes smallest kid |
594 |
|
if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) |
595 |
|
break; |
599 |
|
} |
600 |
|
} |
601 |
|
|
602 |
+ |
/** |
603 |
+ |
* Establishes the heap invariant (described above) in the entire tree, |
604 |
+ |
* assuming nothing about the order of the elements prior to the call. |
605 |
+ |
*/ |
606 |
+ |
private void heapify() { |
607 |
+ |
for (int i = size/2; i >= 1; i--) |
608 |
+ |
fixDown(i); |
609 |
+ |
} |
610 |
|
|
611 |
|
/** |
612 |
|
* Returns the comparator used to order this collection, or <tt>null</tt> |
638 |
|
s.writeInt(queue.length); |
639 |
|
|
640 |
|
// Write out all elements in the proper order. |
641 |
< |
for (int i=0; i<size; i++) |
641 |
> |
for (int i=1; i<=size; i++) |
642 |
|
s.writeObject(queue[i]); |
643 |
|
} |
644 |
|
|
657 |
|
queue = new Object[arrayLength]; |
658 |
|
|
659 |
|
// Read in all elements in the proper order. |
660 |
< |
for (int i=0; i<size; i++) |
661 |
< |
queue[i] = s.readObject(); |
660 |
> |
for (int i=1; i<=size; i++) |
661 |
> |
queue[i] = (E) s.readObject(); |
662 |
|
} |
663 |
|
|
664 |
|
} |
598 |
– |
|