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/* |
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* %W% %E% |
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* |
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* Copyright 2003 Sun Microsystems, Inc. All rights reserved. |
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* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. |
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*/ |
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|
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package java.util; |
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|
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/** |
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* An unbounded priority {@linkplain Queue queue} based on a priority |
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* heap. This queue orders elements according to an order specified |
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* at construction time, which is specified either according to their |
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* <i>natural order</i> (see {@link Comparable}), or according to a |
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* {@link java.util.Comparator}, depending on which constructor is |
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* used. A priority queue does not permit <tt>null</tt> elements. |
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* |
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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 {@link #remove()} and {@link #poll()} |
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* methods remove and return the head of the queue, and the {@link |
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* #element()} and {@link #peek()} methods return, but do not delete, |
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* 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>This class implements all of the <em>optional</em> methods of |
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* the {@link Collection} and {@link Iterator} interfaces. The |
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* Iterator provided in method {@link #iterator()} is <em>not</em> |
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* guaranteed to traverse the elements of the PriorityQueue in any |
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* particular order. If you need ordered traversal, consider using |
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* <tt>Arrays.sort(pq.toArray())</tt>. |
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* |
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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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* |
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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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* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the |
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* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and |
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* constant time for the retrieval methods (<tt>peek</tt>, |
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* <tt>element</tt>, and <tt>size</tt>). |
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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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* Java Collections Framework</a>. |
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* @since 1.5 |
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* @version %I%, %G% |
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* @author Josh Bloch |
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*/ |
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public class PriorityQueue<E> extends AbstractQueue<E> |
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implements Queue<E>, 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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/** |
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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 d |
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* of n, 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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*/ |
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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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*/ |
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private int size = 0; |
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|
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/** |
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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<? 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 transient int modCount = 0; |
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|
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/** |
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* Creates 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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*/ |
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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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/** |
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* Creates 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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* |
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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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/** |
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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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*/ |
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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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this.comparator = comparator; |
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} |
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|
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/** |
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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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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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if (initialCapacity < 1) |
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initialCapacity = 1; |
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|
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this.queue = new Object[initialCapacity + 1]; |
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} |
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|
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/** |
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* Initially fill elements of the queue array under the |
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* knowledge that it is sorted or is another PQ, in which |
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* case we can just place the elements in the order presented. |
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*/ |
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private void fillFromSorted(Collection<? extends E> c) { |
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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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queue[++size] = i.next(); |
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} |
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|
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/** |
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* 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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queue[++size] = i.next(); |
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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 sorted |
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* according to the same comparator, or according to its elements' |
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* natural order if the collection is sorted according to its |
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* elements' natural order. Otherwise, the priority queue is |
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* ordered according to 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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*/ |
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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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// @fixme double-cast workaround for compiler |
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SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)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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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 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. This priority queue will be sorted |
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* according to the same comparator as the given collection, or |
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* according to its elements' natural order if the collection is |
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* sorted according to 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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*/ |
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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 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. This priority queue will be sorted |
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* according to the same comparator as the given collection, or |
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* according to its elements' natural order if the collection is |
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* sorted according to 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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*/ |
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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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Object[] newQueue = new Object[newlen]; |
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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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|
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|
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/** |
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* Inserts the specified element to this priority queue. |
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* |
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* @return <tt>true</tt> |
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* @throws ClassCastException if the specified element cannot be compared |
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* 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 <tt>null</tt>. |
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*/ |
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public boolean offer(E o) { |
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if (o == null) |
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throw new NullPointerException(); |
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modCount++; |
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++size; |
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|
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// Grow backing store if necessary |
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if (size >= queue.length) |
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grow(size); |
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|
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queue[size] = o; |
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fixUp(size); |
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return true; |
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} |
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|
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public E peek() { |
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if (size == 0) |
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return null; |
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return (E) queue[1]; |
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} |
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|
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// Collection Methods - the first two override to update docs |
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|
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/** |
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* Adds the specified element to this queue. |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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* |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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*/ |
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public boolean add(E o) { |
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return offer(o); |
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} |
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|
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|
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/** |
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* Adds all of the elements in the specified collection to this queue. |
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* The behavior of this operation is undefined if |
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* the specified collection is modified while the operation is in |
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* progress. (This implies that the behavior of this call is undefined if |
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* the specified collection is this queue, and this queue is nonempty.) |
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* <p> |
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* This implementation iterates over the specified collection, and adds |
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* each object returned by the iterator to this collection, in turn. |
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* @param c collection whose elements are to be added to this queue |
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* @return <tt>true</tt> if this queue changed as a result of the |
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* call. |
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* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt> |
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* is <tt>null</tt> |
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* @throws ClassCastException if any element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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return super.addAll(c); |
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} |
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|
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public boolean remove(Object o) { |
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if (o == null) |
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return false; |
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|
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if (comparator == null) { |
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for (int i = 1; i <= size; i++) { |
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if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) { |
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removeAt(i); |
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return true; |
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} |
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} |
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} else { |
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for (int i = 1; i <= size; i++) { |
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if (comparator.compare((E)queue[i], (E)o) == 0) { |
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removeAt(i); |
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return true; |
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} |
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} |
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} |
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return false; |
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} |
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|
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/** |
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* Returns an iterator over the elements in this queue. The iterator |
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* does not return the elements in any particular order. |
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* |
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* @return an iterator over the elements in this queue. |
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*/ |
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public Iterator<E> iterator() { |
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return new Itr(); |
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} |
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|
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private class Itr implements Iterator<E> { |
382 |
|
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/** |
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* Index (into queue array) of element to be returned by |
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* subsequent call to next. |
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*/ |
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private int cursor = 1; |
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|
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/** |
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* Index of element returned by most recent call to next, |
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* unless that element came from the forgetMeNot list. |
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* Reset to 0 if element is deleted by a call to remove. |
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*/ |
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private int lastRet = 0; |
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|
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/** |
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* The modCount value that the iterator believes that the backing |
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* List should have. If this expectation is violated, the iterator |
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* has detected concurrent modification. |
400 |
*/ |
401 |
private int expectedModCount = modCount; |
402 |
|
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/** |
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* A list of elements that were moved from the unvisited portion of |
405 |
* the heap into the visited portion as a result of "unlucky" element |
406 |
* removals during the iteration. (Unlucky element removals are those |
407 |
* that require a fixup instead of a fixdown.) We must visit all of |
408 |
* the elements in this list to complete the iteration. We do this |
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* after we've completed the "normal" iteration. |
410 |
* |
411 |
* We expect that most iterations, even those involving removals, |
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* will not use need to store elements in this field. |
413 |
*/ |
414 |
private ArrayList<E> forgetMeNot = null; |
415 |
|
416 |
/** |
417 |
* Element returned by the most recent call to next iff that |
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* element was drawn from the forgetMeNot list. |
419 |
*/ |
420 |
private Object lastRetElt = null; |
421 |
|
422 |
public boolean hasNext() { |
423 |
return cursor <= size || forgetMeNot != null; |
424 |
} |
425 |
|
426 |
public E next() { |
427 |
checkForComodification(); |
428 |
E result; |
429 |
if (cursor <= size) { |
430 |
result = (E) queue[cursor]; |
431 |
lastRet = cursor++; |
432 |
} |
433 |
else if (forgetMeNot == null) |
434 |
throw new NoSuchElementException(); |
435 |
else { |
436 |
int remaining = forgetMeNot.size(); |
437 |
result = forgetMeNot.remove(remaining - 1); |
438 |
if (remaining == 1) |
439 |
forgetMeNot = null; |
440 |
lastRet = 0; |
441 |
lastRetElt = result; |
442 |
} |
443 |
return result; |
444 |
} |
445 |
|
446 |
public void remove() { |
447 |
checkForComodification(); |
448 |
|
449 |
if (lastRet != 0) { |
450 |
E moved = PriorityQueue.this.removeAt(lastRet); |
451 |
lastRet = 0; |
452 |
if (moved == null) { |
453 |
cursor--; |
454 |
} else { |
455 |
if (forgetMeNot == null) |
456 |
forgetMeNot = new ArrayList<E>(); |
457 |
forgetMeNot.add(moved); |
458 |
} |
459 |
} else if (lastRetElt != null) { |
460 |
PriorityQueue.this.remove(lastRetElt); |
461 |
lastRetElt = null; |
462 |
} else { |
463 |
throw new IllegalStateException(); |
464 |
} |
465 |
|
466 |
expectedModCount = modCount; |
467 |
} |
468 |
|
469 |
final void checkForComodification() { |
470 |
if (modCount != expectedModCount) |
471 |
throw new ConcurrentModificationException(); |
472 |
} |
473 |
} |
474 |
|
475 |
public int size() { |
476 |
return size; |
477 |
} |
478 |
|
479 |
/** |
480 |
* Remove all elements from the priority queue. |
481 |
*/ |
482 |
public void clear() { |
483 |
modCount++; |
484 |
|
485 |
// Null out element references to prevent memory leak |
486 |
for (int i=1; i<=size; i++) |
487 |
queue[i] = null; |
488 |
|
489 |
size = 0; |
490 |
} |
491 |
|
492 |
public E poll() { |
493 |
if (size == 0) |
494 |
return null; |
495 |
modCount++; |
496 |
|
497 |
E result = (E) queue[1]; |
498 |
queue[1] = queue[size]; |
499 |
queue[size--] = null; // Drop extra ref to prevent memory leak |
500 |
if (size > 1) |
501 |
fixDown(1); |
502 |
|
503 |
return result; |
504 |
} |
505 |
|
506 |
/** |
507 |
* Removes and returns the ith element from queue. (Recall that queue |
508 |
* is one-based, so 1 <= i <= size.) |
509 |
* |
510 |
* Normally this method leaves the elements at positions from 1 up to i-1, |
511 |
* inclusive, untouched. Under these circumstances, it returns null. |
512 |
* Occasionally, in order to maintain the heap invariant, it must move |
513 |
* the last element of the list to some index in the range [2, i-1], |
514 |
* and move the element previously at position (i/2) to position i. |
515 |
* Under these circumstances, this method returns the element that was |
516 |
* previously at the end of the list and is now at some position between |
517 |
* 2 and i-1 inclusive. |
518 |
*/ |
519 |
private E removeAt(int i) { |
520 |
assert i > 0 && i <= size; |
521 |
modCount++; |
522 |
|
523 |
E moved = (E) queue[size]; |
524 |
queue[i] = moved; |
525 |
queue[size--] = null; // Drop extra ref to prevent memory leak |
526 |
if (i <= size) { |
527 |
fixDown(i); |
528 |
if (queue[i] == moved) { |
529 |
fixUp(i); |
530 |
if (queue[i] != moved) |
531 |
return moved; |
532 |
} |
533 |
} |
534 |
return null; |
535 |
} |
536 |
|
537 |
/** |
538 |
* Establishes the heap invariant (described above) assuming the heap |
539 |
* satisfies the invariant except possibly for the leaf-node indexed by k |
540 |
* (which may have a nextExecutionTime less than its parent's). |
541 |
* |
542 |
* This method functions by "promoting" queue[k] up the hierarchy |
543 |
* (by swapping it with its parent) repeatedly until queue[k] |
544 |
* is greater than or equal to its parent. |
545 |
*/ |
546 |
private void fixUp(int k) { |
547 |
if (comparator == null) { |
548 |
while (k > 1) { |
549 |
int j = k >> 1; |
550 |
if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0) |
551 |
break; |
552 |
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
553 |
k = j; |
554 |
} |
555 |
} else { |
556 |
while (k > 1) { |
557 |
int j = k >>> 1; |
558 |
if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) |
559 |
break; |
560 |
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
561 |
k = j; |
562 |
} |
563 |
} |
564 |
} |
565 |
|
566 |
/** |
567 |
* Establishes the heap invariant (described above) in the subtree |
568 |
* rooted at k, which is assumed to satisfy the heap invariant except |
569 |
* possibly for node k itself (which may be greater than its children). |
570 |
* |
571 |
* This method functions by "demoting" queue[k] down the hierarchy |
572 |
* (by swapping it with its smaller child) repeatedly until queue[k] |
573 |
* is less than or equal to its children. |
574 |
*/ |
575 |
private void fixDown(int k) { |
576 |
int j; |
577 |
if (comparator == null) { |
578 |
while ((j = k << 1) <= size && (j > 0)) { |
579 |
if (j<size && |
580 |
((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
581 |
j++; // j indexes smallest kid |
582 |
|
583 |
if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0) |
584 |
break; |
585 |
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
586 |
k = j; |
587 |
} |
588 |
} else { |
589 |
while ((j = k << 1) <= size && (j > 0)) { |
590 |
if (j<size && |
591 |
comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
592 |
j++; // j indexes smallest kid |
593 |
if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) |
594 |
break; |
595 |
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; |
596 |
k = j; |
597 |
} |
598 |
} |
599 |
} |
600 |
|
601 |
/** |
602 |
* Establishes the heap invariant (described above) in the entire tree, |
603 |
* assuming nothing about the order of the elements prior to the call. |
604 |
*/ |
605 |
private void heapify() { |
606 |
for (int i = size/2; i >= 1; i--) |
607 |
fixDown(i); |
608 |
} |
609 |
|
610 |
/** |
611 |
* Returns the comparator used to order this collection, or <tt>null</tt> |
612 |
* if this collection is sorted according to its elements natural ordering |
613 |
* (using <tt>Comparable</tt>). |
614 |
* |
615 |
* @return the comparator used to order this collection, or <tt>null</tt> |
616 |
* if this collection is sorted according to its elements natural ordering. |
617 |
*/ |
618 |
public Comparator<? super E> comparator() { |
619 |
return comparator; |
620 |
} |
621 |
|
622 |
/** |
623 |
* Save the state of the instance to a stream (that |
624 |
* is, serialize it). |
625 |
* |
626 |
* @serialData The length of the array backing the instance is |
627 |
* emitted (int), followed by all of its elements (each an |
628 |
* <tt>Object</tt>) in the proper order. |
629 |
* @param s the stream |
630 |
*/ |
631 |
private void writeObject(java.io.ObjectOutputStream s) |
632 |
throws java.io.IOException{ |
633 |
// Write out element count, and any hidden stuff |
634 |
s.defaultWriteObject(); |
635 |
|
636 |
// Write out array length |
637 |
s.writeInt(queue.length); |
638 |
|
639 |
// Write out all elements in the proper order. |
640 |
for (int i=1; i<=size; i++) |
641 |
s.writeObject(queue[i]); |
642 |
} |
643 |
|
644 |
/** |
645 |
* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is, |
646 |
* deserialize it). |
647 |
* @param s the stream |
648 |
*/ |
649 |
private void readObject(java.io.ObjectInputStream s) |
650 |
throws java.io.IOException, ClassNotFoundException { |
651 |
// Read in size, and any hidden stuff |
652 |
s.defaultReadObject(); |
653 |
|
654 |
// Read in array length and allocate array |
655 |
int arrayLength = s.readInt(); |
656 |
queue = new Object[arrayLength]; |
657 |
|
658 |
// Read in all elements in the proper order. |
659 |
for (int i=1; i<=size; i++) |
660 |
queue[i] = (E) s.readObject(); |
661 |
} |
662 |
|
663 |
} |