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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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* <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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* |
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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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* An unbounded priority {@linkplain Queue queue} based on a priority |
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* heap. This queue orders elements according to an order specified |
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* at construction time, which is specified either according to their |
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* <i>natural order</i> (see {@link Comparable}), or according to a |
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* {@link java.util.Comparator}, depending on which constructor is |
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* used. A priority queue does not permit <tt>null</tt> elements. |
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* A priority queue relying on natural ordering also does not |
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* permit insertion of non-comparable objects (doing so may result |
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* in <tt>ClassCastException</tt>). |
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* |
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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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* <p>The <em>head</em> of this queue is the <em>least</em> element |
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* with respect to the specified ordering. If multiple elements are |
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* tied for least value, the head is one of those elements -- ties are |
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* broken arbitrarily. The queue retrieval operations <tt>poll</tt>, |
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* <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the |
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* element at 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 an internal |
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* <i>capacity</i> governing the size of an array used 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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* <p>This class implements all of the <em>optional</em> methods of |
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* the {@link Collection} and {@link Iterator} interfaces. The |
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* 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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* particular order. If you need ordered traversal, consider using |
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* <tt>Arrays.sort(pq.toArray())</tt>. |
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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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* @param <E> the type of elements held in this collection |
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*/ |
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public class PriorityQueue<E> extends AbstractQueue<E> |
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implements Queue<E>, java.io.Serializable { |
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private static final long serialVersionUID = -7720805057305804111L; |
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private static final int DEFAULT_INITIAL_CAPACITY = 11; |
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/** |
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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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|
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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 into 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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|
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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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|
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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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*/ |
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public boolean add(E o) { |
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return super.add(o); |
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return offer(o); |
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} |
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|
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|
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/** |
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* Adds all of the elements in the specified collection to this queue. |
329 |
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* The behavior of this operation is undefined if |
330 |
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* the specified collection is modified while the operation is in |
331 |
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* progress. (This implies that the behavior of this call is undefined if |
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* the specified collection is this queue, and this queue is nonempty.) |
333 |
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* <p> |
334 |
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* This implementation iterates over the specified collection, and adds |
335 |
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* each object returned by the iterator to this collection, in turn. |
336 |
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* @throws NullPointerException {@inheritDoc} |
337 |
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* @throws ClassCastException if any element cannot be compared |
338 |
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* with elements currently in the priority queue according |
339 |
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* to the priority queue's ordering. |
340 |
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*/ |
341 |
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public boolean addAll(Collection<? extends E> c) { |
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return super.addAll(c); |
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} |
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|
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– |
|
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– |
/** |
347 |
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* Removes a single instance of the specified element from this |
348 |
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* queue, if it is present. More formally, |
349 |
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* removes an element <tt>e</tt> such that <tt>(o==null ? e==null : |
350 |
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* o.equals(e))</tt>, if the queue contains one or more such |
351 |
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* elements. Returns <tt>true</tt> if the queue contained the |
352 |
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* specified element (or equivalently, if the queue changed as a |
353 |
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* result of the call). |
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* |
355 |
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* <p>This implementation iterates over the queue looking for the |
356 |
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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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} |
339 |
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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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} |
346 |
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} |
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} |
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|
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private class Itr implements Iterator<E> { |
362 |
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|
363 |
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/** |
364 |
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* Index (into queue array) of element to be returned by |
365 |
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* subsequent call to next. |
367 |
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private int cursor = 1; |
368 |
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|
369 |
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/** |
370 |
< |
* Index of element returned by most recent call to next or |
371 |
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* previous. Reset to 0 if this element is deleted by a call |
372 |
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* to remove. |
370 |
> |
* Index of element returned by most recent call to next, |
371 |
> |
* unless that element came from the forgetMeNot list. |
372 |
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* Reset to 0 if element is deleted by a call to remove. |
373 |
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*/ |
374 |
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private int lastRet = 0; |
375 |
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|
380 |
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*/ |
381 |
|
private int expectedModCount = modCount; |
382 |
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|
383 |
+ |
/** |
384 |
+ |
* A list of elements that were moved from the unvisited portion of |
385 |
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* the heap into the visited portion as a result of "unlucky" element |
386 |
+ |
* removals during the iteration. (Unlucky element removals are those |
387 |
+ |
* that require a fixup instead of a fixdown.) We must visit all of |
388 |
+ |
* the elements in this list to complete the iteration. We do this |
389 |
+ |
* after we've completed the "normal" iteration. |
390 |
+ |
* |
391 |
+ |
* We expect that most iterations, even those involving removals, |
392 |
+ |
* will not use need to store elements in this field. |
393 |
+ |
*/ |
394 |
+ |
private ArrayList<E> forgetMeNot = null; |
395 |
+ |
|
396 |
+ |
/** |
397 |
+ |
* Element returned by the most recent call to next iff that |
398 |
+ |
* element was drawn from the forgetMeNot list. |
399 |
+ |
*/ |
400 |
+ |
private Object lastRetElt = null; |
401 |
+ |
|
402 |
|
public boolean hasNext() { |
403 |
< |
return cursor <= size; |
403 |
> |
return cursor <= size || forgetMeNot != null; |
404 |
|
} |
405 |
|
|
406 |
|
public E next() { |
407 |
|
checkForComodification(); |
408 |
< |
if (cursor > size) |
408 |
> |
E result; |
409 |
> |
if (cursor <= size) { |
410 |
> |
result = (E) queue[cursor]; |
411 |
> |
lastRet = cursor++; |
412 |
> |
} |
413 |
> |
else if (forgetMeNot == null) |
414 |
|
throw new NoSuchElementException(); |
415 |
< |
E result = (E) queue[cursor]; |
416 |
< |
lastRet = cursor++; |
415 |
> |
else { |
416 |
> |
int remaining = forgetMeNot.size(); |
417 |
> |
result = forgetMeNot.remove(remaining - 1); |
418 |
> |
if (remaining == 1) |
419 |
> |
forgetMeNot = null; |
420 |
> |
lastRet = 0; |
421 |
> |
lastRetElt = result; |
422 |
> |
} |
423 |
|
return result; |
424 |
|
} |
425 |
|
|
426 |
|
public void remove() { |
427 |
– |
if (lastRet == 0) |
428 |
– |
throw new IllegalStateException(); |
427 |
|
checkForComodification(); |
428 |
|
|
429 |
< |
PriorityQueue.this.remove(lastRet); |
430 |
< |
if (lastRet < cursor) |
431 |
< |
cursor--; |
432 |
< |
lastRet = 0; |
429 |
> |
if (lastRet != 0) { |
430 |
> |
E moved = PriorityQueue.this.removeAt(lastRet); |
431 |
> |
lastRet = 0; |
432 |
> |
if (moved == null) { |
433 |
> |
cursor--; |
434 |
> |
} else { |
435 |
> |
if (forgetMeNot == null) |
436 |
> |
forgetMeNot = new ArrayList<E>(); |
437 |
> |
forgetMeNot.add(moved); |
438 |
> |
} |
439 |
> |
} else if (lastRetElt != null) { |
440 |
> |
PriorityQueue.this.remove(lastRetElt); |
441 |
> |
lastRetElt = null; |
442 |
> |
} else { |
443 |
> |
throw new IllegalStateException(); |
444 |
> |
} |
445 |
> |
|
446 |
|
expectedModCount = modCount; |
447 |
|
} |
448 |
|
|
469 |
|
size = 0; |
470 |
|
} |
471 |
|
|
472 |
+ |
public E poll() { |
473 |
+ |
if (size == 0) |
474 |
+ |
return null; |
475 |
+ |
modCount++; |
476 |
+ |
|
477 |
+ |
E result = (E) queue[1]; |
478 |
+ |
queue[1] = queue[size]; |
479 |
+ |
queue[size--] = null; // Drop extra ref to prevent memory leak |
480 |
+ |
if (size > 1) |
481 |
+ |
fixDown(1); |
482 |
+ |
|
483 |
+ |
return result; |
484 |
+ |
} |
485 |
+ |
|
486 |
|
/** |
487 |
< |
* Removes and returns the ith element from queue. Recall |
488 |
< |
* that queue is one-based, so 1 <= i <= size. |
487 |
> |
* Removes and returns the ith element from queue. (Recall that queue |
488 |
> |
* is one-based, so 1 <= i <= size.) |
489 |
|
* |
490 |
< |
* XXX: Could further special-case i==size, but is it worth it? |
491 |
< |
* XXX: Could special-case i==0, but is it worth it? |
490 |
> |
* Normally this method leaves the elements at positions from 1 up to i-1, |
491 |
> |
* inclusive, untouched. Under these circumstances, it returns null. |
492 |
> |
* Occasionally, in order to maintain the heap invariant, it must move |
493 |
> |
* the last element of the list to some index in the range [2, i-1], |
494 |
> |
* and move the element previously at position (i/2) to position i. |
495 |
> |
* Under these circumstances, this method returns the element that was |
496 |
> |
* previously at the end of the list and is now at some position between |
497 |
> |
* 2 and i-1 inclusive. |
498 |
|
*/ |
499 |
< |
private E remove(int i) { |
500 |
< |
assert i <= size; |
499 |
> |
private E removeAt(int i) { |
500 |
> |
assert i > 0 && i <= size; |
501 |
|
modCount++; |
502 |
|
|
503 |
< |
E result = (E) queue[i]; |
504 |
< |
queue[i] = queue[size]; |
503 |
> |
E moved = (E) queue[size]; |
504 |
> |
queue[i] = moved; |
505 |
|
queue[size--] = null; // Drop extra ref to prevent memory leak |
506 |
< |
if (i <= size) |
506 |
> |
if (i <= size) { |
507 |
|
fixDown(i); |
508 |
< |
return result; |
508 |
> |
if (queue[i] == moved) { |
509 |
> |
fixUp(i); |
510 |
> |
if (queue[i] != moved) |
511 |
> |
return moved; |
512 |
> |
} |
513 |
> |
} |
514 |
> |
return null; |
515 |
|
} |
516 |
|
|
517 |
|
/** |
534 |
|
} |
535 |
|
} else { |
536 |
|
while (k > 1) { |
537 |
< |
int j = k >> 1; |
537 |
> |
int j = k >>> 1; |
538 |
|
if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) |
539 |
|
break; |
540 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
555 |
|
private void fixDown(int k) { |
556 |
|
int j; |
557 |
|
if (comparator == null) { |
558 |
< |
while ((j = k << 1) <= size) { |
559 |
< |
if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
558 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
559 |
> |
if (j<size && |
560 |
> |
((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
561 |
|
j++; // j indexes smallest kid |
562 |
+ |
|
563 |
|
if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0) |
564 |
|
break; |
565 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
566 |
|
k = j; |
567 |
|
} |
568 |
|
} else { |
569 |
< |
while ((j = k << 1) <= size) { |
570 |
< |
if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
569 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
570 |
> |
if (j<size && |
571 |
> |
comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
572 |
|
j++; // j indexes smallest kid |
573 |
|
if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) |
574 |
|
break; |
578 |
|
} |
579 |
|
} |
580 |
|
|
581 |
+ |
/** |
582 |
+ |
* Establishes the heap invariant (described above) in the entire tree, |
583 |
+ |
* assuming nothing about the order of the elements prior to the call. |
584 |
+ |
*/ |
585 |
+ |
private void heapify() { |
586 |
+ |
for (int i = size/2; i >= 1; i--) |
587 |
+ |
fixDown(i); |
588 |
+ |
} |
589 |
|
|
590 |
|
/** |
591 |
|
* Returns the comparator used to order this collection, or <tt>null</tt> |
617 |
|
s.writeInt(queue.length); |
618 |
|
|
619 |
|
// Write out all elements in the proper order. |
620 |
< |
for (int i=0; i<size; i++) |
620 |
> |
for (int i=1; i<=size; i++) |
621 |
|
s.writeObject(queue[i]); |
622 |
|
} |
623 |
|
|
636 |
|
queue = new Object[arrayLength]; |
637 |
|
|
638 |
|
// Read in all elements in the proper order. |
639 |
< |
for (int i=0; i<size; i++) |
640 |
< |
queue[i] = s.readObject(); |
639 |
> |
for (int i=1; i<=size; i++) |
640 |
> |
queue[i] = (E) s.readObject(); |
641 |
|
} |
642 |
|
|
643 |
|
} |
596 |
– |
|