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package java.util; |
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/* |
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* @(#)PriorityQueue.java 1.8 05/08/27 |
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* |
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* Copyright 2005 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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import java.util.*; // for javadoc (till 6280605 is fixed) |
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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 an order specified at construction time, which is |
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* specified in the same manner as {@link java.util.TreeSet} and {@link java.util.TreeMap}: |
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* 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 constructor is used. |
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* The <em>head</em> of this queue is the least element with respect to the |
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* specified ordering. 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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* An unbounded priority {@linkplain Queue queue} based on a priority |
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* heap. The elements of the priority queue are ordered according to |
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* their {@linkplain Comparable natural ordering}, or by a {@link |
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* Comparator} provided at queue construction time, depending on which |
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* constructor is used. A priority queue does not permit |
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* <tt>null</tt> elements. A priority queue relying on natural |
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* ordering also does not permit insertion of non-comparable objects |
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* (doing so may result in <tt>ClassCastException</tt>). |
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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 <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>The {@link #remove()} and {@link #poll()} methods remove and |
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* return the head of the queue. |
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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 {@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>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 <tt>Arrays.sort(pq.toArray())</tt>. |
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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. 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> <strong>Note that this implementation is not synchronized.</strong> |
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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.PriorityBlockingQueue} class. |
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* |
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* <p>Implementation note: this implementation provides O(log(n)) time |
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* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>, |
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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 1.8, 08/27/05 |
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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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implements 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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private transient int modCount = 0; |
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/** |
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* Create a <tt>PriorityQueue</tt> with the default initial capacity |
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* (11) that orders its elements according to their natural |
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* ordering (using <tt>Comparable</tt>.) |
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* Creates a <tt>PriorityQueue</tt> 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, null); |
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} |
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/** |
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* Create a <tt>PriorityQueue</tt> with the specified initial capacity |
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* that orders its elements according to their natural ordering |
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* (using <tt>Comparable</tt>.) |
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* Creates a <tt>PriorityQueue</tt> 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 <tt>initialCapacity</tt> 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 <tt>PriorityQueue</tt> with the specified initial capacity |
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* Creates a <tt>PriorityQueue</tt> 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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* If <tt>null</tt> then the order depends on the elements' natural |
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* ordering. |
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* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less |
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* than 1 |
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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 |
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* this priority queue. If <tt>null</tt>, the <i>natural |
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* ordering</i> of the elements will be used. |
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* @throws IllegalArgumentException if <tt>initialCapacity</tt> is |
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* less than 1 |
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*/ |
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public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) { |
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public PriorityQueue(int initialCapacity, |
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Comparator<? super E> comparator) { |
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if (initialCapacity < 1) |
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throw new IllegalArgumentException(); |
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this.queue = new Object[initialCapacity + 1]; |
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} |
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/** |
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* Create a <tt>PriorityQueue</tt> 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; or 1 if the collection is empty. |
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* 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 |
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* <tt>Sorted</tt>, the priority queue is ordered according to |
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* its elements' natural order. |
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* |
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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 <tt>c</tt> or any element within it |
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* is <tt>null</tt> |
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* Common code to initialize underlying queue array across |
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* constructors below. |
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*/ |
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public PriorityQueue(Collection<? extends E> c) { |
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private void initializeArray(Collection<? extends E> c) { |
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int sz = c.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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initialCapacity = 1; |
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this.queue = new Object[initialCapacity + 1]; |
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} |
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if (c instanceof Sorted) { |
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// FIXME: this code assumes too much |
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this.comparator = (Comparator<? super E>) ((Sorted)c).comparator(); |
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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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* 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 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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int k = ++size; |
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if (k >= queue.length) |
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grow(k); |
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queue[k] = 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 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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int k = ++size; |
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if (k >= queue.length) |
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grow(k); |
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queue[k] = i.next(); |
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} |
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heapify(); |
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} |
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|
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/** |
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* Creates a <tt>PriorityQueue</tt> containing the elements in the |
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* specified collection. The priority queue has an initial |
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* capacity of 110% of the size of the specified collection or 1 |
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* if the collection is empty. If the specified collection is an |
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* instance of a {@link java.util.SortedSet} or is another |
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* <tt>PriorityQueue</tt>, the priority queue will be ordered |
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* according to the same ordering. Otherwise, this priority queue |
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* will be ordered according to the natural ordering of its elements. |
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* |
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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 any |
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* of its elements are null |
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*/ |
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public PriorityQueue(Collection<? extends E> c) { |
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initializeArray(c); |
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if (c instanceof SortedSet) { |
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SortedSet<? extends E> s = (SortedSet<? extends E>)c; |
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comparator = (Comparator<? super E>)s.comparator(); |
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fillFromSorted(s); |
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} else if (c instanceof PriorityQueue) { |
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PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c; |
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comparator = (Comparator<? super E>)s.comparator(); |
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fillFromSorted(s); |
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} else { |
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comparator = null; |
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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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add(i.next()); |
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fillFromUnsorted(c); |
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} |
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} |
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|
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/** |
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* Creates a <tt>PriorityQueue</tt> containing the elements in the |
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* specified priority queue. The priority queue has an initial |
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* capacity of 110% of the size of the specified priority queue or |
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* 1 if the priority queue is empty. 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 <tt>c</tt> cannot be |
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* compared to one another according to <tt>c</tt>'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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public PriorityQueue(PriorityQueue<? extends E> c) { |
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initializeArray(c); |
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comparator = (Comparator<? super E>)c.comparator(); |
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fillFromSorted(c); |
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} |
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|
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/** |
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* Creates a <tt>PriorityQueue</tt> containing the elements in the |
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* specified sorted set. The priority queue has an initial |
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* capacity of 110% of the size of the specified sorted set or 1 |
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* if the sorted set is empty. 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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*/ |
257 |
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public PriorityQueue(SortedSet<? extends E> c) { |
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initializeArray(c); |
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comparator = (Comparator<? super E>)c.comparator(); |
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fillFromSorted(c); |
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} |
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|
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/** |
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* Resize array, if necessary, to be able to hold given index. |
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*/ |
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private void grow(int index) { |
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int newlen = queue.length; |
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if (index < newlen) // don't need to grow |
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return; |
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if (index == Integer.MAX_VALUE) |
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throw new OutOfMemoryError(); |
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while (newlen <= index) { |
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if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow |
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newlen = Integer.MAX_VALUE; |
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else |
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newlen <<= 2; |
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} |
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queue = Arrays.copyOf(queue, newlen); |
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} |
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|
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// Queue Methods |
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/** |
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* Inserts the specified element into this priority queue. |
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* |
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* @return <tt>true</tt> (as specified by {@link Collection#add}) |
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* @throws ClassCastException if the specified element cannot be |
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* compared with elements currently in this priority queue |
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* according to the priority queue's ordering |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean add(E e) { |
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return offer(e); |
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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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* @param element the element to add. |
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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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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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* @throws NullPointerException if the specified element is null. |
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* @return <tt>true</tt> (as specified by {@link Queue#offer}) |
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* @throws ClassCastException if the specified element cannot be |
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* compared with elements currently in this priority queue |
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* according to the priority queue's ordering |
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* @throws NullPointerException if the specified element is null |
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*/ |
303 |
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public boolean offer(E element) { |
304 |
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if (element == null) |
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public boolean offer(E e) { |
304 |
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if (e == null) |
305 |
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throw new NullPointerException(); |
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modCount++; |
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++size; |
308 |
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|
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// Grow backing store if necessary |
310 |
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while (size >= queue.length) { |
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Object[] newQueue = new Object[2 * queue.length]; |
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System.arraycopy(queue, 0, newQueue, 0, queue.length); |
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queue = newQueue; |
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} |
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if (size >= queue.length) |
311 |
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grow(size); |
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|
313 |
< |
queue[size] = element; |
313 |
> |
queue[size] = e; |
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fixUp(size); |
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return true; |
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} |
317 |
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|
318 |
< |
public E poll() { |
318 |
> |
public E peek() { |
319 |
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if (size == 0) |
320 |
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return null; |
189 |
– |
return (E) remove(1); |
190 |
– |
} |
191 |
– |
|
192 |
– |
public E peek() { |
321 |
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return (E) queue[1]; |
322 |
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} |
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|
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// Collection Methods |
325 |
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|
326 |
< |
// these first two override just to get the throws docs |
324 |
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private int indexOf(Object o) { |
325 |
> |
if (o == null) |
326 |
> |
return -1; |
327 |
> |
for (int i = 1; i <= size; i++) |
328 |
> |
if (o.equals(queue[i])) |
329 |
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return i; |
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return -1; |
331 |
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} |
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|
333 |
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/** |
334 |
< |
* @throws NullPointerException if the specified element is <tt>null</tt>. |
335 |
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* @throws ClassCastException if the specified element cannot be compared |
336 |
< |
* with elements currently in the priority queue according |
337 |
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* to the priority queue's ordering. |
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* Removes a single instance of the specified element from this queue, |
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* if it is present. More formally, removes an element <tt>e</tt> such |
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* that <tt>o.equals(e)</tt>, if this queue contains one or more such |
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* elements. Returns true if this queue contained the specified element |
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* (or equivalently, if this queue changed as a result of the call). |
339 |
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* |
340 |
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* @param o element to be removed from this queue, if present |
341 |
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* @return <tt>true</tt> if this queue changed as a result of the call |
342 |
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*/ |
343 |
< |
public boolean add(E element) { |
344 |
< |
return super.add(element); |
343 |
> |
public boolean remove(Object o) { |
344 |
> |
int i = indexOf(o); |
345 |
> |
if (i == -1) |
346 |
> |
return false; |
347 |
> |
else { |
348 |
> |
removeAt(i); |
349 |
> |
return true; |
350 |
> |
} |
351 |
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} |
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|
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/** |
354 |
< |
* @throws NullPointerException if any element is <tt>null</tt>. |
355 |
< |
* @throws ClassCastException if any element cannot be compared |
356 |
< |
* with elements currently in the priority queue according |
357 |
< |
* to the priority queue's ordering. |
354 |
> |
* Returns <tt>true</tt> if this queue contains the specified element. |
355 |
> |
* More formally, returns <tt>true</tt> if and only if this queue contains |
356 |
> |
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
357 |
> |
* |
358 |
> |
* @param o object to be checked for containment in this queue |
359 |
> |
* @return <tt>true</tt> if this queue contains the specified element |
360 |
|
*/ |
361 |
< |
public boolean addAll(Collection<? extends E> c) { |
362 |
< |
return super.addAll(c); |
361 |
> |
public boolean contains(Object o) { |
362 |
> |
return indexOf(o) != -1; |
363 |
|
} |
364 |
|
|
365 |
< |
public boolean remove(Object o) { |
366 |
< |
if (o == null) |
367 |
< |
return false; |
365 |
> |
/** |
366 |
> |
* Returns an array containing all of the elements in this queue, |
367 |
> |
* The elements are in no particular order. |
368 |
> |
* |
369 |
> |
* <p>The returned array will be "safe" in that no references to it are |
370 |
> |
* maintained by this list. (In other words, this method must allocate |
371 |
> |
* a new array). The caller is thus free to modify the returned array. |
372 |
> |
* |
373 |
> |
* @return an array containing all of the elements in this queue. |
374 |
> |
*/ |
375 |
> |
public Object[] toArray() { |
376 |
> |
return Arrays.copyOfRange(queue, 1, size+1); |
377 |
> |
} |
378 |
|
|
379 |
< |
if (comparator == null) { |
380 |
< |
for (int i = 1; i <= size; i++) { |
381 |
< |
if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) { |
382 |
< |
remove(i); |
383 |
< |
return true; |
384 |
< |
} |
385 |
< |
} |
386 |
< |
} else { |
387 |
< |
for (int i = 1; i <= size; i++) { |
388 |
< |
if (comparator.compare((E)queue[i], (E)o) == 0) { |
389 |
< |
remove(i); |
390 |
< |
return true; |
391 |
< |
} |
392 |
< |
} |
393 |
< |
} |
394 |
< |
return false; |
379 |
> |
/** |
380 |
> |
* Returns an array containing all of the elements in this queue. |
381 |
> |
* The elements are in no particular order. The runtime type of |
382 |
> |
* the returned array is that of the specified array. If the queue |
383 |
> |
* fits in the specified array, it is returned therein. |
384 |
> |
* Otherwise, a new array is allocated with the runtime type of |
385 |
> |
* the specified array and the size of this queue. |
386 |
> |
* |
387 |
> |
* <p>If the queue fits in the specified array with room to spare |
388 |
> |
* (i.e., the array has more elements than the queue), the element in |
389 |
> |
* the array immediately following the end of the collection is set to |
390 |
> |
* <tt>null</tt>. (This is useful in determining the length of the |
391 |
> |
* queue <i>only</i> if the caller knows that the queue does not contain |
392 |
> |
* any null elements.) |
393 |
> |
* |
394 |
> |
* @param a the array into which the elements of the queue are to |
395 |
> |
* be stored, if it is big enough; otherwise, a new array of the |
396 |
> |
* same runtime type is allocated for this purpose. |
397 |
> |
* @return an array containing the elements of the queue |
398 |
> |
* @throws ArrayStoreException if the runtime type of the specified array |
399 |
> |
* is not a supertype of the runtime type of every element in |
400 |
> |
* this queue |
401 |
> |
* @throws NullPointerException if the specified array is null |
402 |
> |
*/ |
403 |
> |
public <T> T[] toArray(T[] a) { |
404 |
> |
if (a.length < size) |
405 |
> |
// Make a new array of a's runtime type, but my contents: |
406 |
> |
return (T[]) Arrays.copyOfRange(queue, 1, size+1, a.getClass()); |
407 |
> |
System.arraycopy(queue, 1, a, 0, size); |
408 |
> |
if (a.length > size) |
409 |
> |
a[size] = null; |
410 |
> |
return a; |
411 |
|
} |
412 |
|
|
413 |
+ |
/** |
414 |
+ |
* Returns an iterator over the elements in this queue. The iterator |
415 |
+ |
* does not return the elements in any particular order. |
416 |
+ |
* |
417 |
+ |
* @return an iterator over the elements in this queue |
418 |
+ |
*/ |
419 |
|
public Iterator<E> iterator() { |
420 |
|
return new Itr(); |
421 |
|
} |
422 |
|
|
423 |
|
private class Itr implements Iterator<E> { |
424 |
+ |
|
425 |
|
/** |
426 |
|
* Index (into queue array) of element to be returned by |
427 |
|
* subsequent call to next. |
429 |
|
private int cursor = 1; |
430 |
|
|
431 |
|
/** |
432 |
< |
* Index of element returned by most recent call to next or |
433 |
< |
* previous. Reset to 0 if this element is deleted by a call |
434 |
< |
* to remove. |
432 |
> |
* Index of element returned by most recent call to next, |
433 |
> |
* unless that element came from the forgetMeNot list. |
434 |
> |
* Reset to 0 if element is deleted by a call to remove. |
435 |
|
*/ |
436 |
|
private int lastRet = 0; |
437 |
|
|
442 |
|
*/ |
443 |
|
private int expectedModCount = modCount; |
444 |
|
|
445 |
+ |
/** |
446 |
+ |
* A list of elements that were moved from the unvisited portion of |
447 |
+ |
* the heap into the visited portion as a result of "unlucky" element |
448 |
+ |
* removals during the iteration. (Unlucky element removals are those |
449 |
+ |
* that require a fixup instead of a fixdown.) We must visit all of |
450 |
+ |
* the elements in this list to complete the iteration. We do this |
451 |
+ |
* after we've completed the "normal" iteration. |
452 |
+ |
* |
453 |
+ |
* We expect that most iterations, even those involving removals, |
454 |
+ |
* will not use need to store elements in this field. |
455 |
+ |
*/ |
456 |
+ |
private ArrayList<E> forgetMeNot = null; |
457 |
+ |
|
458 |
+ |
/** |
459 |
+ |
* Element returned by the most recent call to next iff that |
460 |
+ |
* element was drawn from the forgetMeNot list. |
461 |
+ |
*/ |
462 |
+ |
private Object lastRetElt = null; |
463 |
+ |
|
464 |
|
public boolean hasNext() { |
465 |
< |
return cursor <= size; |
465 |
> |
return cursor <= size || forgetMeNot != null; |
466 |
|
} |
467 |
|
|
468 |
|
public E next() { |
469 |
|
checkForComodification(); |
470 |
< |
if (cursor > size) |
470 |
> |
E result; |
471 |
> |
if (cursor <= size) { |
472 |
> |
result = (E) queue[cursor]; |
473 |
> |
lastRet = cursor++; |
474 |
> |
} |
475 |
> |
else if (forgetMeNot == null) |
476 |
|
throw new NoSuchElementException(); |
477 |
< |
E result = (E) queue[cursor]; |
478 |
< |
lastRet = cursor++; |
477 |
> |
else { |
478 |
> |
int remaining = forgetMeNot.size(); |
479 |
> |
result = forgetMeNot.remove(remaining - 1); |
480 |
> |
if (remaining == 1) |
481 |
> |
forgetMeNot = null; |
482 |
> |
lastRet = 0; |
483 |
> |
lastRetElt = result; |
484 |
> |
} |
485 |
|
return result; |
486 |
|
} |
487 |
|
|
488 |
|
public void remove() { |
281 |
– |
if (lastRet == 0) |
282 |
– |
throw new IllegalStateException(); |
489 |
|
checkForComodification(); |
490 |
|
|
491 |
< |
PriorityQueue.this.remove(lastRet); |
492 |
< |
if (lastRet < cursor) |
493 |
< |
cursor--; |
494 |
< |
lastRet = 0; |
491 |
> |
if (lastRet != 0) { |
492 |
> |
E moved = PriorityQueue.this.removeAt(lastRet); |
493 |
> |
lastRet = 0; |
494 |
> |
if (moved == null) { |
495 |
> |
cursor--; |
496 |
> |
} else { |
497 |
> |
if (forgetMeNot == null) |
498 |
> |
forgetMeNot = new ArrayList<E>(); |
499 |
> |
forgetMeNot.add(moved); |
500 |
> |
} |
501 |
> |
} else if (lastRetElt != null) { |
502 |
> |
PriorityQueue.this.remove(lastRetElt); |
503 |
> |
lastRetElt = null; |
504 |
> |
} else { |
505 |
> |
throw new IllegalStateException(); |
506 |
> |
} |
507 |
> |
|
508 |
|
expectedModCount = modCount; |
509 |
|
} |
510 |
|
|
514 |
|
} |
515 |
|
} |
516 |
|
|
298 |
– |
/** |
299 |
– |
* Returns the number of elements in this priority queue. |
300 |
– |
* |
301 |
– |
* @return the number of elements in this priority queue. |
302 |
– |
*/ |
517 |
|
public int size() { |
518 |
|
return size; |
519 |
|
} |
520 |
|
|
521 |
|
/** |
522 |
< |
* Remove all elements from the priority queue. |
522 |
> |
* Removes all of the elements from this priority queue. |
523 |
> |
* The queue will be empty after this call returns. |
524 |
|
*/ |
525 |
|
public void clear() { |
526 |
|
modCount++; |
532 |
|
size = 0; |
533 |
|
} |
534 |
|
|
535 |
+ |
public E poll() { |
536 |
+ |
if (size == 0) |
537 |
+ |
return null; |
538 |
+ |
modCount++; |
539 |
+ |
|
540 |
+ |
E result = (E) queue[1]; |
541 |
+ |
queue[1] = queue[size]; |
542 |
+ |
queue[size--] = null; // Drop extra ref to prevent memory leak |
543 |
+ |
if (size > 1) |
544 |
+ |
fixDown(1); |
545 |
+ |
|
546 |
+ |
return result; |
547 |
+ |
} |
548 |
+ |
|
549 |
|
/** |
550 |
< |
* Removes and returns the ith element from queue. Recall |
551 |
< |
* that queue is one-based, so 1 <= i <= size. |
550 |
> |
* Removes and returns the ith element from queue. (Recall that queue |
551 |
> |
* is one-based, so 1 <= i <= size.) |
552 |
|
* |
553 |
< |
* XXX: Could further special-case i==size, but is it worth it? |
554 |
< |
* XXX: Could special-case i==0, but is it worth it? |
553 |
> |
* Normally this method leaves the elements at positions from 1 up to i-1, |
554 |
> |
* inclusive, untouched. Under these circumstances, it returns null. |
555 |
> |
* Occasionally, in order to maintain the heap invariant, it must move |
556 |
> |
* the last element of the list to some index in the range [2, i-1], |
557 |
> |
* and move the element previously at position (i/2) to position i. |
558 |
> |
* Under these circumstances, this method returns the element that was |
559 |
> |
* previously at the end of the list and is now at some position between |
560 |
> |
* 2 and i-1 inclusive. |
561 |
|
*/ |
562 |
< |
private E remove(int i) { |
563 |
< |
assert i <= size; |
562 |
> |
private E removeAt(int i) { |
563 |
> |
assert i > 0 && i <= size; |
564 |
|
modCount++; |
565 |
|
|
566 |
< |
E result = (E) queue[i]; |
567 |
< |
queue[i] = queue[size]; |
566 |
> |
E moved = (E) queue[size]; |
567 |
> |
queue[i] = moved; |
568 |
|
queue[size--] = null; // Drop extra ref to prevent memory leak |
569 |
< |
if (i <= size) |
569 |
> |
if (i <= size) { |
570 |
|
fixDown(i); |
571 |
< |
return result; |
571 |
> |
if (queue[i] == moved) { |
572 |
> |
fixUp(i); |
573 |
> |
if (queue[i] != moved) |
574 |
> |
return moved; |
575 |
> |
} |
576 |
> |
} |
577 |
> |
return null; |
578 |
|
} |
579 |
|
|
580 |
|
/** |
590 |
|
if (comparator == null) { |
591 |
|
while (k > 1) { |
592 |
|
int j = k >> 1; |
593 |
< |
if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0) |
593 |
> |
if (((Comparable<? super E>)queue[j]).compareTo((E)queue[k]) <= 0) |
594 |
|
break; |
595 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
596 |
|
k = j; |
597 |
|
} |
598 |
|
} else { |
599 |
|
while (k > 1) { |
600 |
< |
int j = k >> 1; |
600 |
> |
int j = k >>> 1; |
601 |
|
if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) |
602 |
|
break; |
603 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
618 |
|
private void fixDown(int k) { |
619 |
|
int j; |
620 |
|
if (comparator == null) { |
621 |
< |
while ((j = k << 1) <= size) { |
622 |
< |
if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
621 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
622 |
> |
if (j<size && |
623 |
> |
((Comparable<? super E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
624 |
|
j++; // j indexes smallest kid |
625 |
< |
if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0) |
625 |
> |
|
626 |
> |
if (((Comparable<? super E>)queue[k]).compareTo((E)queue[j]) <= 0) |
627 |
|
break; |
628 |
|
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
629 |
|
k = j; |
630 |
|
} |
631 |
|
} else { |
632 |
< |
while ((j = k << 1) <= size) { |
633 |
< |
if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
632 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
633 |
> |
if (j<size && |
634 |
> |
comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
635 |
|
j++; // j indexes smallest kid |
636 |
|
if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) |
637 |
|
break; |
641 |
|
} |
642 |
|
} |
643 |
|
|
644 |
+ |
/** |
645 |
+ |
* Establishes the heap invariant (described above) in the entire tree, |
646 |
+ |
* assuming nothing about the order of the elements prior to the call. |
647 |
+ |
*/ |
648 |
+ |
private void heapify() { |
649 |
+ |
for (int i = size/2; i >= 1; i--) |
650 |
+ |
fixDown(i); |
651 |
+ |
} |
652 |
+ |
|
653 |
+ |
/** |
654 |
+ |
* Returns the comparator used to order the elements in this |
655 |
+ |
* queue, or <tt>null</tt> if this queue is sorted according to |
656 |
+ |
* the {@linkplain Comparable natural ordering} of its elements. |
657 |
+ |
* |
658 |
+ |
* @return the comparator used to order this queue, or |
659 |
+ |
* <tt>null</tt> if this queue is sorted according to the |
660 |
+ |
* natural ordering of its elements. |
661 |
+ |
*/ |
662 |
|
public Comparator<? super E> comparator() { |
663 |
|
return comparator; |
664 |
|
} |
672 |
|
* <tt>Object</tt>) in the proper order. |
673 |
|
* @param s the stream |
674 |
|
*/ |
675 |
< |
private synchronized void writeObject(java.io.ObjectOutputStream s) |
675 |
> |
private void writeObject(java.io.ObjectOutputStream s) |
676 |
|
throws java.io.IOException{ |
677 |
|
// Write out element count, and any hidden stuff |
678 |
|
s.defaultWriteObject(); |
681 |
|
s.writeInt(queue.length); |
682 |
|
|
683 |
|
// Write out all elements in the proper order. |
684 |
< |
for (int i=0; i<size; i++) |
684 |
> |
for (int i=1; i<=size; i++) |
685 |
|
s.writeObject(queue[i]); |
686 |
|
} |
687 |
|
|
688 |
|
/** |
689 |
< |
* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is, |
690 |
< |
* deserialize it). |
689 |
> |
* Reconstitute the <tt>PriorityQueue</tt> instance from a stream |
690 |
> |
* (that is, deserialize it). |
691 |
|
* @param s the stream |
692 |
|
*/ |
693 |
< |
private synchronized void readObject(java.io.ObjectInputStream s) |
693 |
> |
private void readObject(java.io.ObjectInputStream s) |
694 |
|
throws java.io.IOException, ClassNotFoundException { |
695 |
|
// Read in size, and any hidden stuff |
696 |
|
s.defaultReadObject(); |
700 |
|
queue = new Object[arrayLength]; |
701 |
|
|
702 |
|
// Read in all elements in the proper order. |
703 |
< |
for (int i=0; i<size; i++) |
704 |
< |
queue[i] = s.readObject(); |
703 |
> |
for (int i=1; i<=size; i++) |
704 |
> |
queue[i] = (E) s.readObject(); |
705 |
|
} |
706 |
|
|
707 |
|
} |
446 |
– |
|