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package java.util; |
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/* |
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* Todo |
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* Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Sun designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Sun in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* 1) Make it serializable. |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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package java.util; |
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|
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/** |
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* An unbounded priority queue based on a priority heap. This queue orders |
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* elements according to the order specified at creation time. This order is |
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* specified as for {@link TreeSet} and {@link 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 Comparator}, depending on which constructor is used. |
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* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the |
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* minimal element with respect to the specified ordering. If multiple |
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* these elements are tied for least value, no guarantees are made as to |
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* which of elements is returned. |
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* |
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* <p>Each priority queue has a <i>capacity</i>. The capacity is the size of |
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* the array used to store the elements on the queue. It is always at least |
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* as large as the queue size. As elements are added to a priority list, |
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* its capacity grows automatically. The details of the growth policy are not |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* The elements of the priority queue are ordered according to their |
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* {@linkplain Comparable natural ordering}, or by a {@link Comparator} |
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* provided at queue construction time, depending on which constructor is |
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* used. A priority queue does not permit {@code null} elements. |
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* A priority queue relying on natural ordering also does not permit |
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* insertion of non-comparable objects (doing so may result in |
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* {@code ClassCastException}). |
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* |
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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 {@code poll}, |
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* {@code remove}, {@code peek}, and {@code element} 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 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>Implementation note: this implementation provides O(log(n)) time for |
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* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt> |
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* methods; linear time for the <tt>remove(Object)</tt> and |
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* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>, |
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* <tt>element</tt>, and <tt>size</tt> methods. |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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* Iterator} interfaces. The Iterator provided in method {@link |
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* #iterator()} is <em>not</em> guaranteed to traverse the elements of |
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* the priority queue in any particular order. If you need ordered |
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* traversal, consider using {@code Arrays.sort(pq.toArray())}. |
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* |
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* <p> <strong>Note that this implementation is not synchronized.</strong> |
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* Multiple threads should not access a {@code PriorityQueue} |
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* instance concurrently if any of the threads modifies the queue. |
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* Instead, use the thread-safe {@link |
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* java.util.concurrent.PriorityBlockingQueue} class. |
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* |
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* <p>Implementation note: this implementation provides |
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* O(log(n)) time for the enqueing and dequeing methods |
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* ({@code offer}, {@code poll}, {@code remove()} and {@code add}); |
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* linear time for the {@code remove(Object)} and {@code contains(Object)} |
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* methods; and constant time for the retrieval methods |
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* ({@code peek}, {@code element}, and {@code size}). |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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* @author Josh Bloch, Doug Lea |
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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> |
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{ |
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implements java.io.Serializable { |
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|
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private static final long serialVersionUID = -7720805057305804111L; |
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|
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private static final int DEFAULT_INITIAL_CAPACITY = 11; |
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/** |
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* Priority queue represented as a balanced binary heap: the two children |
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* of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is |
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* ordered by comparator, or by the elements' natural ordering, if |
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* comparator is null: For each node n in the heap, and each descendant |
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* of n, d, n <= d. |
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* |
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* The element with the lowest value is in queue[1] (assuming the queue is |
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* nonempty). A one-based array is used in preference to the traditional |
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* zero-based array to simplify parent and child calculations. |
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* |
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* queue.length must be >= 2, even if size == 0. |
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* Priority queue represented as a balanced binary heap: the two |
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* children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The |
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* priority queue is ordered by comparator, or by the elements' |
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* natural ordering, if comparator is null: For each node n in the |
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* heap and each descendant d of n, n <= d. The element with the |
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* lowest value is in queue[0], assuming the queue is nonempty. |
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*/ |
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private E[] queue; |
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private transient Object[] queue; |
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|
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/** |
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* The number of elements in the priority queue. |
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* The comparator, or null if priority queue uses elements' |
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* natural ordering. |
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*/ |
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private final Comparator<E> comparator; |
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private final Comparator<? super E> comparator; |
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|
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/** |
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* The number of times this priority queue has been |
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* <i>structurally modified</i>. See AbstractList for gory details. |
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*/ |
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private int modCount = 0; |
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private transient int modCount = 0; |
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|
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/** |
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* Create a new priority queue with the default initial capacity (11) |
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* that orders its elements according to their natural ordering. |
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* Creates a {@code PriorityQueue} with the default initial |
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* capacity (11) that orders its elements according to their |
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* {@linkplain Comparable natural ordering}. |
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*/ |
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public PriorityQueue() { |
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this(DEFAULT_INITIAL_CAPACITY); |
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this(DEFAULT_INITIAL_CAPACITY, null); |
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} |
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/** |
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* Create a new priority queue with the specified initial capacity |
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* that orders its elements according to their natural ordering. |
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* Creates a {@code PriorityQueue} with the specified initial |
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* capacity that orders its elements according to their |
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* {@linkplain Comparable natural ordering}. |
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* |
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* @param initialCapacity the initial capacity for this priority queue. |
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* @param initialCapacity the initial capacity for this priority queue |
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* @throws IllegalArgumentException if {@code initialCapacity} is less |
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* than 1 |
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*/ |
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public PriorityQueue(int initialCapacity) { |
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this(initialCapacity, null); |
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} |
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/** |
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* Create a new priority queue with the specified initial capacity (11) |
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* Creates a {@code PriorityQueue} with the specified initial capacity |
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* that orders its elements according to the specified comparator. |
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* |
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* @param initialCapacity the initial capacity for this priority queue. |
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* @param comparator the comparator used to order this priority queue. |
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*/ |
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public PriorityQueue(int initialCapacity, Comparator<E> comparator) { |
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* @param initialCapacity the initial capacity for this priority queue |
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* @param comparator the comparator that will be used to order this |
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* priority queue. If {@code null}, the {@linkplain Comparable |
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* natural ordering} of the elements will be used. |
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* @throws IllegalArgumentException if {@code initialCapacity} is |
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* less than 1 |
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*/ |
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public PriorityQueue(int initialCapacity, |
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Comparator<? super E> comparator) { |
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// Note: This restriction of at least one is not actually needed, |
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// but continues for 1.5 compatibility |
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if (initialCapacity < 1) |
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initialCapacity = 1; |
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queue = new E[initialCapacity + 1]; |
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throw new IllegalArgumentException(); |
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this.queue = new Object[initialCapacity]; |
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this.comparator = comparator; |
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} |
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|
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/** |
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* Create a new priority queue containing the elements in the specified |
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* collection. The priority queue has an initial capacity of 110% of the |
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* size of the specified collection. If the specified collection |
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* implements the {@link Sorted} interface, the priority queue will be |
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* sorted according to the same comparator, or according to its elements' |
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* natural order if the collection is sorted according to its elements' |
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* natural order. If the specified collection does not implement the |
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* <tt>Sorted</tt> interface, the priority queue is ordered according to |
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* its elements' natural order. |
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* Creates a {@code PriorityQueue} containing the elements in the |
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* specified collection. If the specified collection is an instance of |
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* a {@link SortedSet} or is another {@code PriorityQueue}, this |
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* priority queue will be ordered according to the same ordering. |
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* Otherwise, this priority queue will be ordered according to the |
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* {@linkplain Comparable natural ordering} of its elements. |
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* |
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* @param initialElements the collection whose elements are to be placed |
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* into this priority queue. |
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* @param c the collection whose elements are to be placed |
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* into this priority queue |
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* @throws ClassCastException if elements of the specified collection |
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* cannot be compared to one another according to the priority |
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* queue's ordering. |
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* @throws NullPointerException if the specified collection or an |
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* element of the specified collection is <tt>null</tt>. |
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*/ |
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public PriorityQueue(Collection<E> initialElements) { |
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int sz = initialElements.size(); |
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int initialCapacity = (int)Math.min((sz * 110L) / 100, |
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Integer.MAX_VALUE - 1); |
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if (initialCapacity < 1) |
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initialCapacity = 1; |
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queue = new E[initialCapacity + 1]; |
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* queue's ordering |
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* @throws NullPointerException if the specified collection or any |
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* of its elements are null |
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*/ |
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@SuppressWarnings("unchecked") |
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public PriorityQueue(Collection<? extends E> c) { |
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if (c instanceof SortedSet<?>) { |
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SortedSet<? extends E> ss = (SortedSet<? extends E>) c; |
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this.comparator = (Comparator<? super E>) ss.comparator(); |
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initElementsFromCollection(ss); |
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} |
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else if (c instanceof PriorityQueue<?>) { |
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PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c; |
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this.comparator = (Comparator<? super E>) pq.comparator(); |
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initFromPriorityQueue(pq); |
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} |
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else { |
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this.comparator = null; |
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initFromCollection(c); |
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} |
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} |
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|
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/** |
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* Creates a {@code PriorityQueue} containing the elements in the |
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* specified priority queue. This priority queue will be |
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* ordered according to the same ordering as the given priority |
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* queue. |
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* |
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* @param c the priority queue whose elements are to be placed |
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* into this priority queue |
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* @throws ClassCastException if elements of {@code c} cannot be |
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* compared to one another according to {@code c}'s |
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* ordering |
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* @throws NullPointerException if the specified priority queue or any |
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* of its elements are null |
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*/ |
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@SuppressWarnings("unchecked") |
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public PriorityQueue(PriorityQueue<? extends E> c) { |
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this.comparator = (Comparator<? super E>) c.comparator(); |
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initFromPriorityQueue(c); |
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} |
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|
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if (initialElements instanceof Sorted) { |
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comparator = ((Sorted)initialElements).comparator(); |
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for (Iterator<E> i = initialElements.iterator(); i.hasNext(); ) |
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queue[++size] = i.next(); |
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/** |
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* Creates a {@code PriorityQueue} containing the elements in the |
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* specified sorted set. This priority queue will be ordered |
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* according to the same ordering as the given sorted set. |
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* |
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* @param c the sorted set whose elements are to be placed |
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* into this priority queue |
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* @throws ClassCastException if elements of the specified sorted |
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* set cannot be compared to one another according to the |
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* sorted set's ordering |
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* @throws NullPointerException if the specified sorted set or any |
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* of its elements are null |
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*/ |
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@SuppressWarnings("unchecked") |
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public PriorityQueue(SortedSet<? extends E> c) { |
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this.comparator = (Comparator<? super E>) c.comparator(); |
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initElementsFromCollection(c); |
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} |
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|
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private void initFromPriorityQueue(PriorityQueue<? extends E> c) { |
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if (c.getClass() == PriorityQueue.class) { |
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this.queue = c.toArray(); |
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this.size = c.size(); |
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} else { |
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comparator = null; |
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for (Iterator<E> i = initialElements.iterator(); i.hasNext(); ) |
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add(i.next()); |
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initFromCollection(c); |
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} |
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} |
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|
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// Queue Methods |
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private void initElementsFromCollection(Collection<? extends E> c) { |
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Object[] a = c.toArray(); |
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// If c.toArray incorrectly doesn't return Object[], copy it. |
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if (a.getClass() != Object[].class) |
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a = Arrays.copyOf(a, a.length, Object[].class); |
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int len = a.length; |
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if (len == 1 || this.comparator != null) |
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for (int i = 0; i < len; i++) |
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if (a[i] == null) |
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throw new NullPointerException(); |
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this.queue = a; |
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this.size = a.length; |
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} |
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|
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/** |
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* Remove and return the minimal element from this priority queue if |
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* it contains one or more elements, otherwise <tt>null</tt>. The term |
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* <i>minimal</i> is defined according to this priority queue's order. |
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* Initializes queue array with elements from the given Collection. |
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* |
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* @return the minimal element from this priority queue if it contains |
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* one or more elements, otherwise <tt>null</tt>. |
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> |
* @param c the collection |
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|
*/ |
258 |
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public E poll() { |
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if (size == 0) |
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return null; |
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return remove(1); |
258 |
> |
private void initFromCollection(Collection<? extends E> c) { |
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initElementsFromCollection(c); |
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> |
heapify(); |
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} |
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|
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> |
/** |
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* The maximum size of array to allocate. |
265 |
> |
* Some VMs reserve some header words in an array. |
266 |
> |
* Attempts to allocate larger arrays may result in |
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> |
* OutOfMemoryError: Requested array size exceeds VM limit |
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*/ |
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private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; |
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|
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> |
/** |
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* Increases the capacity of the array. |
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* |
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* @param minCapacity the desired minimum capacity |
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*/ |
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> |
private void grow(int minCapacity) { |
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> |
int oldCapacity = queue.length; |
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> |
// Double size if small; else grow by 50% |
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> |
int newCapacity = oldCapacity + ((oldCapacity < 64) ? |
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> |
(oldCapacity + 2) : |
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> |
(oldCapacity >> 1)); |
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// overflow-conscious code |
283 |
> |
if (newCapacity - MAX_ARRAY_SIZE > 0) |
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> |
newCapacity = hugeCapacity(minCapacity); |
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queue = Arrays.copyOf(queue, newCapacity); |
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} |
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|
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private static int hugeCapacity(int minCapacity) { |
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if (minCapacity < 0) // overflow |
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throw new OutOfMemoryError(); |
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> |
return (minCapacity > MAX_ARRAY_SIZE) ? |
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Integer.MAX_VALUE : |
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> |
MAX_ARRAY_SIZE; |
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|
} |
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|
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/** |
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* Return, but do not remove, the minimal element from the priority queue, |
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< |
* or <tt>null</tt> if the queue is empty. The term <i>minimal</i> is |
162 |
< |
* defined according to this priority queue's order. This method returns |
163 |
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* the same object reference that would be returned by by the |
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* <tt>poll</tt> method. The two methods differ in that this method |
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* does not remove the element from the priority queue. |
297 |
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* Inserts the specified element into this priority queue. |
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|
* |
299 |
< |
* @return the minimal element from this priority queue if it contains |
300 |
< |
* one or more elements, otherwise <tt>null</tt>. |
299 |
> |
* @return {@code true} (as specified by {@link Collection#add}) |
300 |
> |
* @throws ClassCastException if the specified element cannot be |
301 |
> |
* compared with elements currently in this priority queue |
302 |
> |
* according to the priority queue's ordering |
303 |
> |
* @throws NullPointerException if the specified element is null |
304 |
|
*/ |
305 |
+ |
public boolean add(E e) { |
306 |
+ |
return offer(e); |
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+ |
} |
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|
309 |
+ |
/** |
310 |
+ |
* Inserts the specified element into this priority queue. |
311 |
+ |
* |
312 |
+ |
* @return {@code true} (as specified by {@link Queue#offer}) |
313 |
+ |
* @throws ClassCastException if the specified element cannot be |
314 |
+ |
* compared with elements currently in this priority queue |
315 |
+ |
* according to the priority queue's ordering |
316 |
+ |
* @throws NullPointerException if the specified element is null |
317 |
+ |
*/ |
318 |
+ |
public boolean offer(E e) { |
319 |
+ |
if (e == null) |
320 |
+ |
throw new NullPointerException(); |
321 |
+ |
modCount++; |
322 |
+ |
int i = size; |
323 |
+ |
if (i >= queue.length) |
324 |
+ |
grow(i + 1); |
325 |
+ |
size = i + 1; |
326 |
+ |
if (i == 0) |
327 |
+ |
queue[0] = e; |
328 |
+ |
else |
329 |
+ |
siftUp(i, e); |
330 |
+ |
return true; |
331 |
+ |
} |
332 |
+ |
|
333 |
|
public E peek() { |
334 |
< |
return queue[1]; |
334 |
> |
if (size == 0) |
335 |
> |
return null; |
336 |
> |
return (E) queue[0]; |
337 |
|
} |
338 |
|
|
339 |
< |
// Collection Methods |
339 |
> |
private int indexOf(Object o) { |
340 |
> |
if (o != null) { |
341 |
> |
for (int i = 0; i < size; i++) |
342 |
> |
if (o.equals(queue[i])) |
343 |
> |
return i; |
344 |
> |
} |
345 |
> |
return -1; |
346 |
> |
} |
347 |
|
|
348 |
|
/** |
349 |
< |
* Removes a single instance of the specified element from this priority |
350 |
< |
* queue, if it is present. Returns true if this collection contained the |
351 |
< |
* specified element (or equivalently, if this collection changed as a |
349 |
> |
* Removes a single instance of the specified element from this queue, |
350 |
> |
* if it is present. More formally, removes an element {@code e} such |
351 |
> |
* that {@code o.equals(e)}, if this queue contains one or more such |
352 |
> |
* elements. Returns {@code true} if and only if this queue contained |
353 |
> |
* the specified element (or equivalently, if this queue changed as a |
354 |
|
* result of the call). |
355 |
|
* |
356 |
< |
* @param o element to be removed from this collection, if present. |
357 |
< |
* @return <tt>true</tt> if this collection changed as a result of the |
184 |
< |
* call |
185 |
< |
* @throws ClassCastException if the specified element cannot be compared |
186 |
< |
* with elements currently in the priority queue according |
187 |
< |
* to the priority queue's ordering. |
188 |
< |
* @throws NullPointerException if the specified element is null. |
356 |
> |
* @param o element to be removed from this queue, if present |
357 |
> |
* @return {@code true} if this queue changed as a result of the call |
358 |
|
*/ |
359 |
< |
public boolean remove(Object element) { |
360 |
< |
if (element == null) |
361 |
< |
throw new NullPointerException(); |
359 |
> |
public boolean remove(Object o) { |
360 |
> |
int i = indexOf(o); |
361 |
> |
if (i == -1) |
362 |
> |
return false; |
363 |
> |
else { |
364 |
> |
removeAt(i); |
365 |
> |
return true; |
366 |
> |
} |
367 |
> |
} |
368 |
|
|
369 |
< |
if (comparator == null) { |
370 |
< |
for (int i = 1; i <= size; i++) { |
371 |
< |
if (((Comparable)queue[i]).compareTo(element) == 0) { |
372 |
< |
remove(i); |
373 |
< |
return true; |
374 |
< |
} |
375 |
< |
} |
376 |
< |
} else { |
377 |
< |
for (int i = 1; i <= size; i++) { |
378 |
< |
if (comparator.compare(queue[i], (E) element) == 0) { |
379 |
< |
remove(i); |
380 |
< |
return true; |
206 |
< |
} |
369 |
> |
/** |
370 |
> |
* Version of remove using reference equality, not equals. |
371 |
> |
* Needed by iterator.remove. |
372 |
> |
* |
373 |
> |
* @param o element to be removed from this queue, if present |
374 |
> |
* @return {@code true} if removed |
375 |
> |
*/ |
376 |
> |
boolean removeEq(Object o) { |
377 |
> |
for (int i = 0; i < size; i++) { |
378 |
> |
if (o == queue[i]) { |
379 |
> |
removeAt(i); |
380 |
> |
return true; |
381 |
|
} |
382 |
|
} |
383 |
|
return false; |
384 |
|
} |
385 |
|
|
386 |
|
/** |
387 |
< |
* Returns an iterator over the elements in this priority queue. The |
388 |
< |
* first element returned by this iterator is the same element that |
389 |
< |
* would be returned by a call to <tt>peek</tt>. |
387 |
> |
* Returns {@code true} if this queue contains the specified element. |
388 |
> |
* More formally, returns {@code true} if and only if this queue contains |
389 |
> |
* at least one element {@code e} such that {@code o.equals(e)}. |
390 |
> |
* |
391 |
> |
* @param o object to be checked for containment in this queue |
392 |
> |
* @return {@code true} if this queue contains the specified element |
393 |
> |
*/ |
394 |
> |
public boolean contains(Object o) { |
395 |
> |
return indexOf(o) != -1; |
396 |
> |
} |
397 |
> |
|
398 |
> |
/** |
399 |
> |
* Returns an array containing all of the elements in this queue. |
400 |
> |
* The elements are in no particular order. |
401 |
> |
* |
402 |
> |
* <p>The returned array will be "safe" in that no references to it are |
403 |
> |
* maintained by this queue. (In other words, this method must allocate |
404 |
> |
* a new array). The caller is thus free to modify the returned array. |
405 |
> |
* |
406 |
> |
* <p>This method acts as bridge between array-based and collection-based |
407 |
> |
* APIs. |
408 |
|
* |
409 |
< |
* @return an <tt>Iterator</tt> over the elements in this priority queue. |
409 |
> |
* @return an array containing all of the elements in this queue |
410 |
> |
*/ |
411 |
> |
public Object[] toArray() { |
412 |
> |
return Arrays.copyOf(queue, size); |
413 |
> |
} |
414 |
> |
|
415 |
> |
/** |
416 |
> |
* Returns an array containing all of the elements in this queue; the |
417 |
> |
* runtime type of the returned array is that of the specified array. |
418 |
> |
* The returned array elements are in no particular order. |
419 |
> |
* If the queue fits in the specified array, it is returned therein. |
420 |
> |
* Otherwise, a new array is allocated with the runtime type of the |
421 |
> |
* specified array and the size of this queue. |
422 |
> |
* |
423 |
> |
* <p>If the queue fits in the specified array with room to spare |
424 |
> |
* (i.e., the array has more elements than the queue), the element in |
425 |
> |
* the array immediately following the end of the collection is set to |
426 |
> |
* {@code null}. |
427 |
> |
* |
428 |
> |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
429 |
> |
* array-based and collection-based APIs. Further, this method allows |
430 |
> |
* precise control over the runtime type of the output array, and may, |
431 |
> |
* under certain circumstances, be used to save allocation costs. |
432 |
> |
* |
433 |
> |
* <p>Suppose <tt>x</tt> is a queue known to contain only strings. |
434 |
> |
* The following code can be used to dump the queue into a newly |
435 |
> |
* allocated array of <tt>String</tt>: |
436 |
> |
* |
437 |
> |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
438 |
> |
* |
439 |
> |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
440 |
> |
* <tt>toArray()</tt>. |
441 |
> |
* |
442 |
> |
* @param a the array into which the elements of the queue are to |
443 |
> |
* be stored, if it is big enough; otherwise, a new array of the |
444 |
> |
* same runtime type is allocated for this purpose. |
445 |
> |
* @return an array containing all of the elements in this queue |
446 |
> |
* @throws ArrayStoreException if the runtime type of the specified array |
447 |
> |
* is not a supertype of the runtime type of every element in |
448 |
> |
* this queue |
449 |
> |
* @throws NullPointerException if the specified array is null |
450 |
> |
*/ |
451 |
> |
public <T> T[] toArray(T[] a) { |
452 |
> |
if (a.length < size) |
453 |
> |
// Make a new array of a's runtime type, but my contents: |
454 |
> |
return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
455 |
> |
System.arraycopy(queue, 0, a, 0, size); |
456 |
> |
if (a.length > size) |
457 |
> |
a[size] = null; |
458 |
> |
return a; |
459 |
> |
} |
460 |
> |
|
461 |
> |
/** |
462 |
> |
* Returns an iterator over the elements in this queue. The iterator |
463 |
> |
* does not return the elements in any particular order. |
464 |
> |
* |
465 |
> |
* @return an iterator over the elements in this queue |
466 |
|
*/ |
467 |
|
public Iterator<E> iterator() { |
468 |
|
return new Itr(); |
469 |
|
} |
470 |
|
|
471 |
< |
private class Itr implements Iterator<E> { |
471 |
> |
private final class Itr implements Iterator<E> { |
472 |
|
/** |
473 |
|
* Index (into queue array) of element to be returned by |
474 |
|
* subsequent call to next. |
475 |
|
*/ |
476 |
< |
int cursor = 1; |
476 |
> |
private int cursor = 0; |
477 |
> |
|
478 |
> |
/** |
479 |
> |
* Index of element returned by most recent call to next, |
480 |
> |
* unless that element came from the forgetMeNot list. |
481 |
> |
* Set to -1 if element is deleted by a call to remove. |
482 |
> |
*/ |
483 |
> |
private int lastRet = -1; |
484 |
> |
|
485 |
> |
/** |
486 |
> |
* A queue of elements that were moved from the unvisited portion of |
487 |
> |
* the heap into the visited portion as a result of "unlucky" element |
488 |
> |
* removals during the iteration. (Unlucky element removals are those |
489 |
> |
* that require a siftup instead of a siftdown.) We must visit all of |
490 |
> |
* the elements in this list to complete the iteration. We do this |
491 |
> |
* after we've completed the "normal" iteration. |
492 |
> |
* |
493 |
> |
* We expect that most iterations, even those involving removals, |
494 |
> |
* will not need to store elements in this field. |
495 |
> |
*/ |
496 |
> |
private ArrayDeque<E> forgetMeNot = null; |
497 |
|
|
498 |
|
/** |
499 |
< |
* Index of element returned by most recent call to next or |
500 |
< |
* previous. Reset to 0 if this element is deleted by a call |
233 |
< |
* to remove. |
499 |
> |
* Element returned by the most recent call to next iff that |
500 |
> |
* element was drawn from the forgetMeNot list. |
501 |
|
*/ |
502 |
< |
int lastRet = 0; |
502 |
> |
private E lastRetElt = null; |
503 |
|
|
504 |
|
/** |
505 |
|
* The modCount value that the iterator believes that the backing |
506 |
< |
* List should have. If this expectation is violated, the iterator |
506 |
> |
* Queue should have. If this expectation is violated, the iterator |
507 |
|
* has detected concurrent modification. |
508 |
|
*/ |
509 |
< |
int expectedModCount = modCount; |
509 |
> |
private int expectedModCount = modCount; |
510 |
|
|
511 |
|
public boolean hasNext() { |
512 |
< |
return cursor <= size; |
512 |
> |
return cursor < size || |
513 |
> |
(forgetMeNot != null && !forgetMeNot.isEmpty()); |
514 |
|
} |
515 |
|
|
516 |
|
public E next() { |
517 |
< |
checkForComodification(); |
518 |
< |
if (cursor > size) |
519 |
< |
throw new NoSuchElementException(); |
520 |
< |
E result = queue[cursor]; |
521 |
< |
lastRet = cursor++; |
522 |
< |
return result; |
517 |
> |
if (expectedModCount != modCount) |
518 |
> |
throw new ConcurrentModificationException(); |
519 |
> |
if (cursor < size) |
520 |
> |
return (E) queue[lastRet = cursor++]; |
521 |
> |
if (forgetMeNot != null) { |
522 |
> |
lastRet = -1; |
523 |
> |
lastRetElt = forgetMeNot.poll(); |
524 |
> |
if (lastRetElt != null) |
525 |
> |
return lastRetElt; |
526 |
> |
} |
527 |
> |
throw new NoSuchElementException(); |
528 |
|
} |
529 |
|
|
530 |
|
public void remove() { |
531 |
< |
if (lastRet == 0) |
531 |
> |
if (expectedModCount != modCount) |
532 |
> |
throw new ConcurrentModificationException(); |
533 |
> |
if (lastRet != -1) { |
534 |
> |
E moved = PriorityQueue.this.removeAt(lastRet); |
535 |
> |
lastRet = -1; |
536 |
> |
if (moved == null) |
537 |
> |
cursor--; |
538 |
> |
else { |
539 |
> |
if (forgetMeNot == null) |
540 |
> |
forgetMeNot = new ArrayDeque<E>(); |
541 |
> |
forgetMeNot.add(moved); |
542 |
> |
} |
543 |
> |
} else if (lastRetElt != null) { |
544 |
> |
PriorityQueue.this.removeEq(lastRetElt); |
545 |
> |
lastRetElt = null; |
546 |
> |
} else { |
547 |
|
throw new IllegalStateException(); |
548 |
< |
checkForComodification(); |
261 |
< |
|
262 |
< |
PriorityQueue.this.remove(lastRet); |
263 |
< |
if (lastRet < cursor) |
264 |
< |
cursor--; |
265 |
< |
lastRet = 0; |
548 |
> |
} |
549 |
|
expectedModCount = modCount; |
550 |
|
} |
268 |
– |
|
269 |
– |
final void checkForComodification() { |
270 |
– |
if (modCount != expectedModCount) |
271 |
– |
throw new ConcurrentModificationException(); |
272 |
– |
} |
551 |
|
} |
552 |
|
|
275 |
– |
/** |
276 |
– |
* Returns the number of elements in this priority queue. |
277 |
– |
* |
278 |
– |
* @return the number of elements in this priority queue. |
279 |
– |
*/ |
553 |
|
public int size() { |
554 |
|
return size; |
555 |
|
} |
556 |
|
|
557 |
|
/** |
558 |
< |
* Add the specified element to this priority queue. |
559 |
< |
* |
287 |
< |
* @param element the element to add. |
288 |
< |
* @return true |
289 |
< |
* @throws ClassCastException if the specified element cannot be compared |
290 |
< |
* with elements currently in the priority queue according |
291 |
< |
* to the priority queue's ordering. |
292 |
< |
* @throws NullPointerException if the specified element is null. |
558 |
> |
* Removes all of the elements from this priority queue. |
559 |
> |
* The queue will be empty after this call returns. |
560 |
|
*/ |
561 |
< |
public boolean offer(E element) { |
295 |
< |
if (element == null) |
296 |
< |
throw new NullPointerException(); |
561 |
> |
public void clear() { |
562 |
|
modCount++; |
563 |
+ |
for (int i = 0; i < size; i++) |
564 |
+ |
queue[i] = null; |
565 |
+ |
size = 0; |
566 |
+ |
} |
567 |
|
|
568 |
< |
// Grow backing store if necessary |
569 |
< |
if (++size == queue.length) { |
570 |
< |
E[] newQueue = new E[2 * queue.length]; |
571 |
< |
System.arraycopy(queue, 0, newQueue, 0, size); |
572 |
< |
queue = newQueue; |
573 |
< |
} |
574 |
< |
|
575 |
< |
queue[size] = element; |
576 |
< |
fixUp(size); |
577 |
< |
return true; |
568 |
> |
public E poll() { |
569 |
> |
if (size == 0) |
570 |
> |
return null; |
571 |
> |
int s = --size; |
572 |
> |
modCount++; |
573 |
> |
E result = (E) queue[0]; |
574 |
> |
E x = (E) queue[s]; |
575 |
> |
queue[s] = null; |
576 |
> |
if (s != 0) |
577 |
> |
siftDown(0, x); |
578 |
> |
return result; |
579 |
|
} |
580 |
|
|
581 |
|
/** |
582 |
< |
* Remove all elements from the priority queue. |
582 |
> |
* Removes the ith element from queue. |
583 |
> |
* |
584 |
> |
* Normally this method leaves the elements at up to i-1, |
585 |
> |
* inclusive, untouched. Under these circumstances, it returns |
586 |
> |
* null. Occasionally, in order to maintain the heap invariant, |
587 |
> |
* it must swap a later element of the list with one earlier than |
588 |
> |
* i. Under these circumstances, this method returns the element |
589 |
> |
* that was previously at the end of the list and is now at some |
590 |
> |
* position before i. This fact is used by iterator.remove so as to |
591 |
> |
* avoid missing traversing elements. |
592 |
|
*/ |
593 |
< |
public void clear() { |
593 |
> |
private E removeAt(int i) { |
594 |
> |
assert i >= 0 && i < size; |
595 |
|
modCount++; |
596 |
< |
|
597 |
< |
// Null out element references to prevent memory leak |
318 |
< |
for (int i=1; i<=size; i++) |
596 |
> |
int s = --size; |
597 |
> |
if (s == i) // removed last element |
598 |
|
queue[i] = null; |
599 |
< |
|
600 |
< |
size = 0; |
599 |
> |
else { |
600 |
> |
E moved = (E) queue[s]; |
601 |
> |
queue[s] = null; |
602 |
> |
siftDown(i, moved); |
603 |
> |
if (queue[i] == moved) { |
604 |
> |
siftUp(i, moved); |
605 |
> |
if (queue[i] != moved) |
606 |
> |
return moved; |
607 |
> |
} |
608 |
> |
} |
609 |
> |
return null; |
610 |
|
} |
611 |
|
|
612 |
|
/** |
613 |
< |
* Removes and returns the ith element from queue. Recall |
614 |
< |
* that queue is one-based, so 1 <= i <= size. |
613 |
> |
* Inserts item x at position k, maintaining heap invariant by |
614 |
> |
* promoting x up the tree until it is greater than or equal to |
615 |
> |
* its parent, or is the root. |
616 |
> |
* |
617 |
> |
* To simplify and speed up coercions and comparisons. the |
618 |
> |
* Comparable and Comparator versions are separated into different |
619 |
> |
* methods that are otherwise identical. (Similarly for siftDown.) |
620 |
|
* |
621 |
< |
* XXX: Could further special-case i==size, but is it worth it? |
622 |
< |
* XXX: Could special-case i==0, but is it worth it? |
621 |
> |
* @param k the position to fill |
622 |
> |
* @param x the item to insert |
623 |
|
*/ |
624 |
< |
private E remove(int i) { |
625 |
< |
assert i <= size; |
626 |
< |
modCount++; |
624 |
> |
private void siftUp(int k, E x) { |
625 |
> |
if (comparator != null) |
626 |
> |
siftUpUsingComparator(k, x); |
627 |
> |
else |
628 |
> |
siftUpComparable(k, x); |
629 |
> |
} |
630 |
|
|
631 |
< |
E result = queue[i]; |
632 |
< |
queue[i] = queue[size]; |
633 |
< |
queue[size--] = null; // Drop extra ref to prevent memory leak |
634 |
< |
if (i <= size) |
635 |
< |
fixDown(i); |
636 |
< |
return result; |
631 |
> |
private void siftUpComparable(int k, E x) { |
632 |
> |
Comparable<? super E> key = (Comparable<? super E>) x; |
633 |
> |
while (k > 0) { |
634 |
> |
int parent = (k - 1) >>> 1; |
635 |
> |
Object e = queue[parent]; |
636 |
> |
if (key.compareTo((E) e) >= 0) |
637 |
> |
break; |
638 |
> |
queue[k] = e; |
639 |
> |
k = parent; |
640 |
> |
} |
641 |
> |
queue[k] = key; |
642 |
|
} |
643 |
|
|
644 |
< |
/** |
645 |
< |
* Establishes the heap invariant (described above) assuming the heap |
646 |
< |
* satisfies the invariant except possibly for the leaf-node indexed by k |
647 |
< |
* (which may have a nextExecutionTime less than its parent's). |
648 |
< |
* |
649 |
< |
* This method functions by "promoting" queue[k] up the hierarchy |
650 |
< |
* (by swapping it with its parent) repeatedly until queue[k] |
651 |
< |
* is greater than or equal to its parent. |
351 |
< |
*/ |
352 |
< |
private void fixUp(int k) { |
353 |
< |
if (comparator == null) { |
354 |
< |
while (k > 1) { |
355 |
< |
int j = k >> 1; |
356 |
< |
if (((Comparable)queue[j]).compareTo(queue[k]) <= 0) |
357 |
< |
break; |
358 |
< |
E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
359 |
< |
k = j; |
360 |
< |
} |
361 |
< |
} else { |
362 |
< |
while (k > 1) { |
363 |
< |
int j = k >> 1; |
364 |
< |
if (comparator.compare(queue[j], queue[k]) <= 0) |
365 |
< |
break; |
366 |
< |
E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
367 |
< |
k = j; |
368 |
< |
} |
644 |
> |
private void siftUpUsingComparator(int k, E x) { |
645 |
> |
while (k > 0) { |
646 |
> |
int parent = (k - 1) >>> 1; |
647 |
> |
Object e = queue[parent]; |
648 |
> |
if (comparator.compare(x, (E) e) >= 0) |
649 |
> |
break; |
650 |
> |
queue[k] = e; |
651 |
> |
k = parent; |
652 |
|
} |
653 |
+ |
queue[k] = x; |
654 |
|
} |
655 |
|
|
656 |
|
/** |
657 |
< |
* Establishes the heap invariant (described above) in the subtree |
658 |
< |
* rooted at k, which is assumed to satisfy the heap invariant except |
659 |
< |
* possibly for node k itself (which may be greater than its children). |
660 |
< |
* |
661 |
< |
* This method functions by "demoting" queue[k] down the hierarchy |
662 |
< |
* (by swapping it with its smaller child) repeatedly until queue[k] |
663 |
< |
* is less than or equal to its children. |
664 |
< |
*/ |
665 |
< |
private void fixDown(int k) { |
666 |
< |
int j; |
667 |
< |
if (comparator == null) { |
668 |
< |
while ((j = k << 1) <= size) { |
669 |
< |
if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0) |
670 |
< |
j++; // j indexes smallest kid |
671 |
< |
if (((Comparable)queue[k]).compareTo(queue[j]) <= 0) |
672 |
< |
break; |
673 |
< |
E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
674 |
< |
k = j; |
675 |
< |
} |
676 |
< |
} else { |
677 |
< |
while ((j = k << 1) <= size) { |
678 |
< |
if (j < size && comparator.compare(queue[j], queue[j+1]) > 0) |
679 |
< |
j++; // j indexes smallest kid |
680 |
< |
if (comparator.compare(queue[k], queue[j]) <= 0) |
681 |
< |
break; |
682 |
< |
E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
683 |
< |
k = j; |
684 |
< |
} |
657 |
> |
* Inserts item x at position k, maintaining heap invariant by |
658 |
> |
* demoting x down the tree repeatedly until it is less than or |
659 |
> |
* equal to its children or is a leaf. |
660 |
> |
* |
661 |
> |
* @param k the position to fill |
662 |
> |
* @param x the item to insert |
663 |
> |
*/ |
664 |
> |
private void siftDown(int k, E x) { |
665 |
> |
if (comparator != null) |
666 |
> |
siftDownUsingComparator(k, x); |
667 |
> |
else |
668 |
> |
siftDownComparable(k, x); |
669 |
> |
} |
670 |
> |
|
671 |
> |
private void siftDownComparable(int k, E x) { |
672 |
> |
Comparable<? super E> key = (Comparable<? super E>)x; |
673 |
> |
int half = size >>> 1; // loop while a non-leaf |
674 |
> |
while (k < half) { |
675 |
> |
int child = (k << 1) + 1; // assume left child is least |
676 |
> |
Object c = queue[child]; |
677 |
> |
int right = child + 1; |
678 |
> |
if (right < size && |
679 |
> |
((Comparable<? super E>) c).compareTo((E) queue[right]) > 0) |
680 |
> |
c = queue[child = right]; |
681 |
> |
if (key.compareTo((E) c) <= 0) |
682 |
> |
break; |
683 |
> |
queue[k] = c; |
684 |
> |
k = child; |
685 |
|
} |
686 |
+ |
queue[k] = key; |
687 |
+ |
} |
688 |
+ |
|
689 |
+ |
private void siftDownUsingComparator(int k, E x) { |
690 |
+ |
int half = size >>> 1; |
691 |
+ |
while (k < half) { |
692 |
+ |
int child = (k << 1) + 1; |
693 |
+ |
Object c = queue[child]; |
694 |
+ |
int right = child + 1; |
695 |
+ |
if (right < size && |
696 |
+ |
comparator.compare((E) c, (E) queue[right]) > 0) |
697 |
+ |
c = queue[child = right]; |
698 |
+ |
if (comparator.compare(x, (E) c) <= 0) |
699 |
+ |
break; |
700 |
+ |
queue[k] = c; |
701 |
+ |
k = child; |
702 |
+ |
} |
703 |
+ |
queue[k] = x; |
704 |
|
} |
705 |
|
|
706 |
|
/** |
707 |
< |
* Returns the comparator associated with this priority queue, or |
708 |
< |
* <tt>null</tt> if it uses its elements' natural ordering. |
707 |
> |
* Establishes the heap invariant (described above) in the entire tree, |
708 |
> |
* assuming nothing about the order of the elements prior to the call. |
709 |
> |
*/ |
710 |
> |
private void heapify() { |
711 |
> |
for (int i = (size >>> 1) - 1; i >= 0; i--) |
712 |
> |
siftDown(i, (E) queue[i]); |
713 |
> |
} |
714 |
> |
|
715 |
> |
/** |
716 |
> |
* Returns the comparator used to order the elements in this |
717 |
> |
* queue, or {@code null} if this queue is sorted according to |
718 |
> |
* the {@linkplain Comparable natural ordering} of its elements. |
719 |
|
* |
720 |
< |
* @return the comparator associated with this priority queue, or |
721 |
< |
* <tt>null</tt> if it uses its elements' natural ordering. |
720 |
> |
* @return the comparator used to order this queue, or |
721 |
> |
* {@code null} if this queue is sorted according to the |
722 |
> |
* natural ordering of its elements |
723 |
|
*/ |
724 |
< |
Comparator<E> comparator() { |
724 |
> |
public Comparator<? super E> comparator() { |
725 |
|
return comparator; |
726 |
|
} |
727 |
+ |
|
728 |
+ |
/** |
729 |
+ |
* Saves the state of the instance to a stream (that |
730 |
+ |
* is, serializes it). |
731 |
+ |
* |
732 |
+ |
* @serialData The length of the array backing the instance is |
733 |
+ |
* emitted (int), followed by all of its elements |
734 |
+ |
* (each an {@code Object}) in the proper order. |
735 |
+ |
* @param s the stream |
736 |
+ |
*/ |
737 |
+ |
private void writeObject(java.io.ObjectOutputStream s) |
738 |
+ |
throws java.io.IOException{ |
739 |
+ |
// Write out element count, and any hidden stuff |
740 |
+ |
s.defaultWriteObject(); |
741 |
+ |
|
742 |
+ |
// Write out array length, for compatibility with 1.5 version |
743 |
+ |
s.writeInt(Math.max(2, size + 1)); |
744 |
+ |
|
745 |
+ |
// Write out all elements in the "proper order". |
746 |
+ |
for (int i = 0; i < size; i++) |
747 |
+ |
s.writeObject(queue[i]); |
748 |
+ |
} |
749 |
+ |
|
750 |
+ |
/** |
751 |
+ |
* Reconstitutes the {@code PriorityQueue} instance from a stream |
752 |
+ |
* (that is, deserializes it). |
753 |
+ |
* |
754 |
+ |
* @param s the stream |
755 |
+ |
*/ |
756 |
+ |
private void readObject(java.io.ObjectInputStream s) |
757 |
+ |
throws java.io.IOException, ClassNotFoundException { |
758 |
+ |
// Read in size, and any hidden stuff |
759 |
+ |
s.defaultReadObject(); |
760 |
+ |
|
761 |
+ |
// Read in (and discard) array length |
762 |
+ |
s.readInt(); |
763 |
+ |
|
764 |
+ |
queue = new Object[size]; |
765 |
+ |
|
766 |
+ |
// Read in all elements. |
767 |
+ |
for (int i = 0; i < size; i++) |
768 |
+ |
queue[i] = s.readObject(); |
769 |
+ |
|
770 |
+ |
// Elements are guaranteed to be in "proper order", but the |
771 |
+ |
// spec has never explained what that might be. |
772 |
+ |
heapify(); |
773 |
+ |
} |
774 |
|
} |