jaroslav@633: /*
jaroslav@633:  * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
jaroslav@633:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@633:  *
jaroslav@633:  * This code is free software; you can redistribute it and/or modify it
jaroslav@633:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@633:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@633:  * particular file as subject to the "Classpath" exception as provided
jaroslav@633:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@633:  *
jaroslav@633:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@633:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@633:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@633:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@633:  * accompanied this code).
jaroslav@633:  *
jaroslav@633:  * You should have received a copy of the GNU General Public License version
jaroslav@633:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@633:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@633:  *
jaroslav@633:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@633:  * or visit www.oracle.com if you need additional information or have any
jaroslav@633:  * questions.
jaroslav@633:  */
jaroslav@633: 
jaroslav@633: package java.util;
jaroslav@633: 
jaroslav@635: 
jaroslav@633: /**
jaroslav@633:  * An unbounded priority {@linkplain Queue queue} based on a priority heap.
jaroslav@633:  * The elements of the priority queue are ordered according to their
jaroslav@633:  * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
jaroslav@633:  * provided at queue construction time, depending on which constructor is
jaroslav@633:  * used.  A priority queue does not permit {@code null} elements.
jaroslav@633:  * A priority queue relying on natural ordering also does not permit
jaroslav@633:  * insertion of non-comparable objects (doing so may result in
jaroslav@633:  * {@code ClassCastException}).
jaroslav@633:  *
jaroslav@633:  * <p>The <em>head</em> of this queue is the <em>least</em> element
jaroslav@633:  * with respect to the specified ordering.  If multiple elements are
jaroslav@633:  * tied for least value, the head is one of those elements -- ties are
jaroslav@633:  * broken arbitrarily.  The queue retrieval operations {@code poll},
jaroslav@633:  * {@code remove}, {@code peek}, and {@code element} access the
jaroslav@633:  * element at the head of the queue.
jaroslav@633:  *
jaroslav@633:  * <p>A priority queue is unbounded, but has an internal
jaroslav@633:  * <i>capacity</i> governing the size of an array used to store the
jaroslav@633:  * elements on the queue.  It is always at least as large as the queue
jaroslav@633:  * size.  As elements are added to a priority queue, its capacity
jaroslav@633:  * grows automatically.  The details of the growth policy are not
jaroslav@633:  * specified.
jaroslav@633:  *
jaroslav@633:  * <p>This class and its iterator implement all of the
jaroslav@633:  * <em>optional</em> methods of the {@link Collection} and {@link
jaroslav@633:  * Iterator} interfaces.  The Iterator provided in method {@link
jaroslav@633:  * #iterator()} is <em>not</em> guaranteed to traverse the elements of
jaroslav@633:  * the priority queue in any particular order. If you need ordered
jaroslav@633:  * traversal, consider using {@code Arrays.sort(pq.toArray())}.
jaroslav@633:  *
jaroslav@633:  * <p> <strong>Note that this implementation is not synchronized.</strong>
jaroslav@633:  * Multiple threads should not access a {@code PriorityQueue}
jaroslav@633:  * instance concurrently if any of the threads modifies the queue.
jaroslav@633:  * Instead, use the thread-safe {@link
jaroslav@633:  * java.util.concurrent.PriorityBlockingQueue} class.
jaroslav@633:  *
jaroslav@633:  * <p>Implementation note: this implementation provides
jaroslav@633:  * O(log(n)) time for the enqueing and dequeing methods
jaroslav@633:  * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
jaroslav@633:  * linear time for the {@code remove(Object)} and {@code contains(Object)}
jaroslav@633:  * methods; and constant time for the retrieval methods
jaroslav@633:  * ({@code peek}, {@code element}, and {@code size}).
jaroslav@633:  *
jaroslav@633:  * <p>This class is a member of the
jaroslav@633:  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
jaroslav@633:  * Java Collections Framework</a>.
jaroslav@633:  *
jaroslav@633:  * @since 1.5
jaroslav@633:  * @author Josh Bloch, Doug Lea
jaroslav@633:  * @param <E> the type of elements held in this collection
jaroslav@633:  */
jaroslav@633: public class PriorityQueue<E> extends AbstractQueue<E>
jaroslav@633:     implements java.io.Serializable {
jaroslav@633: 
jaroslav@633:     private static final long serialVersionUID = -7720805057305804111L;
jaroslav@633: 
jaroslav@633:     private static final int DEFAULT_INITIAL_CAPACITY = 11;
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Priority queue represented as a balanced binary heap: the two
jaroslav@633:      * children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
jaroslav@633:      * priority queue is ordered by comparator, or by the elements'
jaroslav@633:      * natural ordering, if comparator is null: For each node n in the
jaroslav@633:      * heap and each descendant d of n, n <= d.  The element with the
jaroslav@633:      * lowest value is in queue[0], assuming the queue is nonempty.
jaroslav@633:      */
jaroslav@633:     private transient Object[] queue;
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * The number of elements in the priority queue.
jaroslav@633:      */
jaroslav@633:     private int size = 0;
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * The comparator, or null if priority queue uses elements'
jaroslav@633:      * natural ordering.
jaroslav@633:      */
jaroslav@633:     private final Comparator<? super E> comparator;
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * The number of times this priority queue has been
jaroslav@633:      * <i>structurally modified</i>.  See AbstractList for gory details.
jaroslav@633:      */
jaroslav@633:     private transient int modCount = 0;
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Creates a {@code PriorityQueue} with the default initial
jaroslav@633:      * capacity (11) that orders its elements according to their
jaroslav@633:      * {@linkplain Comparable natural ordering}.
jaroslav@633:      */
jaroslav@633:     public PriorityQueue() {
jaroslav@633:         this(DEFAULT_INITIAL_CAPACITY, null);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Creates a {@code PriorityQueue} with the specified initial
jaroslav@633:      * capacity that orders its elements according to their
jaroslav@633:      * {@linkplain Comparable natural ordering}.
jaroslav@633:      *
jaroslav@633:      * @param initialCapacity the initial capacity for this priority queue
jaroslav@633:      * @throws IllegalArgumentException if {@code initialCapacity} is less
jaroslav@633:      *         than 1
jaroslav@633:      */
jaroslav@633:     public PriorityQueue(int initialCapacity) {
jaroslav@633:         this(initialCapacity, null);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Creates a {@code PriorityQueue} with the specified initial capacity
jaroslav@633:      * that orders its elements according to the specified comparator.
jaroslav@633:      *
jaroslav@633:      * @param  initialCapacity the initial capacity for this priority queue
jaroslav@633:      * @param  comparator the comparator that will be used to order this
jaroslav@633:      *         priority queue.  If {@code null}, the {@linkplain Comparable
jaroslav@633:      *         natural ordering} of the elements will be used.
jaroslav@633:      * @throws IllegalArgumentException if {@code initialCapacity} is
jaroslav@633:      *         less than 1
jaroslav@633:      */
jaroslav@633:     public PriorityQueue(int initialCapacity,
jaroslav@633:                          Comparator<? super E> comparator) {
jaroslav@633:         // Note: This restriction of at least one is not actually needed,
jaroslav@633:         // but continues for 1.5 compatibility
jaroslav@633:         if (initialCapacity < 1)
jaroslav@633:             throw new IllegalArgumentException();
jaroslav@633:         this.queue = new Object[initialCapacity];
jaroslav@633:         this.comparator = comparator;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Creates a {@code PriorityQueue} containing the elements in the
jaroslav@633:      * specified collection.  If the specified collection is an instance of
jaroslav@633:      * a {@link SortedSet} or is another {@code PriorityQueue}, this
jaroslav@633:      * priority queue will be ordered according to the same ordering.
jaroslav@633:      * Otherwise, this priority queue will be ordered according to the
jaroslav@633:      * {@linkplain Comparable natural ordering} of its elements.
jaroslav@633:      *
jaroslav@633:      * @param  c the collection whose elements are to be placed
jaroslav@633:      *         into this priority queue
jaroslav@633:      * @throws ClassCastException if elements of the specified collection
jaroslav@633:      *         cannot be compared to one another according to the priority
jaroslav@633:      *         queue's ordering
jaroslav@633:      * @throws NullPointerException if the specified collection or any
jaroslav@633:      *         of its elements are null
jaroslav@633:      */
jaroslav@633:     @SuppressWarnings("unchecked")
jaroslav@633:     public PriorityQueue(Collection<? extends E> c) {
jaroslav@633:         if (c instanceof SortedSet<?>) {
jaroslav@633:             SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
jaroslav@633:             this.comparator = (Comparator<? super E>) ss.comparator();
jaroslav@633:             initElementsFromCollection(ss);
jaroslav@633:         }
jaroslav@633:         else if (c instanceof PriorityQueue<?>) {
jaroslav@633:             PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
jaroslav@633:             this.comparator = (Comparator<? super E>) pq.comparator();
jaroslav@633:             initFromPriorityQueue(pq);
jaroslav@633:         }
jaroslav@633:         else {
jaroslav@633:             this.comparator = null;
jaroslav@633:             initFromCollection(c);
jaroslav@633:         }
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Creates a {@code PriorityQueue} containing the elements in the
jaroslav@633:      * specified priority queue.  This priority queue will be
jaroslav@633:      * ordered according to the same ordering as the given priority
jaroslav@633:      * queue.
jaroslav@633:      *
jaroslav@633:      * @param  c the priority queue whose elements are to be placed
jaroslav@633:      *         into this priority queue
jaroslav@633:      * @throws ClassCastException if elements of {@code c} cannot be
jaroslav@633:      *         compared to one another according to {@code c}'s
jaroslav@633:      *         ordering
jaroslav@633:      * @throws NullPointerException if the specified priority queue or any
jaroslav@633:      *         of its elements are null
jaroslav@633:      */
jaroslav@633:     @SuppressWarnings("unchecked")
jaroslav@633:     public PriorityQueue(PriorityQueue<? extends E> c) {
jaroslav@633:         this.comparator = (Comparator<? super E>) c.comparator();
jaroslav@633:         initFromPriorityQueue(c);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Creates a {@code PriorityQueue} containing the elements in the
jaroslav@633:      * specified sorted set.   This priority queue will be ordered
jaroslav@633:      * according to the same ordering as the given sorted set.
jaroslav@633:      *
jaroslav@633:      * @param  c the sorted set whose elements are to be placed
jaroslav@633:      *         into this priority queue
jaroslav@633:      * @throws ClassCastException if elements of the specified sorted
jaroslav@633:      *         set cannot be compared to one another according to the
jaroslav@633:      *         sorted set's ordering
jaroslav@633:      * @throws NullPointerException if the specified sorted set or any
jaroslav@633:      *         of its elements are null
jaroslav@633:      */
jaroslav@633:     @SuppressWarnings("unchecked")
jaroslav@633:     public PriorityQueue(SortedSet<? extends E> c) {
jaroslav@633:         this.comparator = (Comparator<? super E>) c.comparator();
jaroslav@633:         initElementsFromCollection(c);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
jaroslav@633:         if (c.getClass() == PriorityQueue.class) {
jaroslav@633:             this.queue = c.toArray();
jaroslav@633:             this.size = c.size();
jaroslav@633:         } else {
jaroslav@633:             initFromCollection(c);
jaroslav@633:         }
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private void initElementsFromCollection(Collection<? extends E> c) {
jaroslav@633:         Object[] a = c.toArray();
jaroslav@633:         // If c.toArray incorrectly doesn't return Object[], copy it.
jaroslav@633:         if (a.getClass() != Object[].class)
jaroslav@633:             a = Arrays.copyOf(a, a.length, Object[].class);
jaroslav@633:         int len = a.length;
jaroslav@633:         if (len == 1 || this.comparator != null)
jaroslav@633:             for (int i = 0; i < len; i++)
jaroslav@633:                 if (a[i] == null)
jaroslav@633:                     throw new NullPointerException();
jaroslav@633:         this.queue = a;
jaroslav@633:         this.size = a.length;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Initializes queue array with elements from the given Collection.
jaroslav@633:      *
jaroslav@633:      * @param c the collection
jaroslav@633:      */
jaroslav@633:     private void initFromCollection(Collection<? extends E> c) {
jaroslav@633:         initElementsFromCollection(c);
jaroslav@633:         heapify();
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * The maximum size of array to allocate.
jaroslav@633:      * Some VMs reserve some header words in an array.
jaroslav@633:      * Attempts to allocate larger arrays may result in
jaroslav@633:      * OutOfMemoryError: Requested array size exceeds VM limit
jaroslav@633:      */
jaroslav@633:     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Increases the capacity of the array.
jaroslav@633:      *
jaroslav@633:      * @param minCapacity the desired minimum capacity
jaroslav@633:      */
jaroslav@633:     private void grow(int minCapacity) {
jaroslav@633:         int oldCapacity = queue.length;
jaroslav@633:         // Double size if small; else grow by 50%
jaroslav@633:         int newCapacity = oldCapacity + ((oldCapacity < 64) ?
jaroslav@633:                                          (oldCapacity + 2) :
jaroslav@633:                                          (oldCapacity >> 1));
jaroslav@633:         // overflow-conscious code
jaroslav@633:         if (newCapacity - MAX_ARRAY_SIZE > 0)
jaroslav@633:             newCapacity = hugeCapacity(minCapacity);
jaroslav@633:         queue = Arrays.copyOf(queue, newCapacity);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private static int hugeCapacity(int minCapacity) {
jaroslav@633:         if (minCapacity < 0) // overflow
jaroslav@633:             throw new OutOfMemoryError();
jaroslav@633:         return (minCapacity > MAX_ARRAY_SIZE) ?
jaroslav@633:             Integer.MAX_VALUE :
jaroslav@633:             MAX_ARRAY_SIZE;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Inserts the specified element into this priority queue.
jaroslav@633:      *
jaroslav@633:      * @return {@code true} (as specified by {@link Collection#add})
jaroslav@633:      * @throws ClassCastException if the specified element cannot be
jaroslav@633:      *         compared with elements currently in this priority queue
jaroslav@633:      *         according to the priority queue's ordering
jaroslav@633:      * @throws NullPointerException if the specified element is null
jaroslav@633:      */
jaroslav@633:     public boolean add(E e) {
jaroslav@633:         return offer(e);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Inserts the specified element into this priority queue.
jaroslav@633:      *
jaroslav@633:      * @return {@code true} (as specified by {@link Queue#offer})
jaroslav@633:      * @throws ClassCastException if the specified element cannot be
jaroslav@633:      *         compared with elements currently in this priority queue
jaroslav@633:      *         according to the priority queue's ordering
jaroslav@633:      * @throws NullPointerException if the specified element is null
jaroslav@633:      */
jaroslav@633:     public boolean offer(E e) {
jaroslav@633:         if (e == null)
jaroslav@633:             throw new NullPointerException();
jaroslav@633:         modCount++;
jaroslav@633:         int i = size;
jaroslav@633:         if (i >= queue.length)
jaroslav@633:             grow(i + 1);
jaroslav@633:         size = i + 1;
jaroslav@633:         if (i == 0)
jaroslav@633:             queue[0] = e;
jaroslav@633:         else
jaroslav@633:             siftUp(i, e);
jaroslav@633:         return true;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     public E peek() {
jaroslav@633:         if (size == 0)
jaroslav@633:             return null;
jaroslav@633:         return (E) queue[0];
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private int indexOf(Object o) {
jaroslav@633:         if (o != null) {
jaroslav@633:             for (int i = 0; i < size; i++)
jaroslav@633:                 if (o.equals(queue[i]))
jaroslav@633:                     return i;
jaroslav@633:         }
jaroslav@633:         return -1;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Removes a single instance of the specified element from this queue,
jaroslav@633:      * if it is present.  More formally, removes an element {@code e} such
jaroslav@633:      * that {@code o.equals(e)}, if this queue contains one or more such
jaroslav@633:      * elements.  Returns {@code true} if and only if this queue contained
jaroslav@633:      * the specified element (or equivalently, if this queue changed as a
jaroslav@633:      * result of the call).
jaroslav@633:      *
jaroslav@633:      * @param o element to be removed from this queue, if present
jaroslav@633:      * @return {@code true} if this queue changed as a result of the call
jaroslav@633:      */
jaroslav@633:     public boolean remove(Object o) {
jaroslav@633:         int i = indexOf(o);
jaroslav@633:         if (i == -1)
jaroslav@633:             return false;
jaroslav@633:         else {
jaroslav@633:             removeAt(i);
jaroslav@633:             return true;
jaroslav@633:         }
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Version of remove using reference equality, not equals.
jaroslav@633:      * Needed by iterator.remove.
jaroslav@633:      *
jaroslav@633:      * @param o element to be removed from this queue, if present
jaroslav@633:      * @return {@code true} if removed
jaroslav@633:      */
jaroslav@633:     boolean removeEq(Object o) {
jaroslav@633:         for (int i = 0; i < size; i++) {
jaroslav@633:             if (o == queue[i]) {
jaroslav@633:                 removeAt(i);
jaroslav@633:                 return true;
jaroslav@633:             }
jaroslav@633:         }
jaroslav@633:         return false;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Returns {@code true} if this queue contains the specified element.
jaroslav@633:      * More formally, returns {@code true} if and only if this queue contains
jaroslav@633:      * at least one element {@code e} such that {@code o.equals(e)}.
jaroslav@633:      *
jaroslav@633:      * @param o object to be checked for containment in this queue
jaroslav@633:      * @return {@code true} if this queue contains the specified element
jaroslav@633:      */
jaroslav@633:     public boolean contains(Object o) {
jaroslav@633:         return indexOf(o) != -1;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Returns an array containing all of the elements in this queue.
jaroslav@633:      * The elements are in no particular order.
jaroslav@633:      *
jaroslav@633:      * <p>The returned array will be "safe" in that no references to it are
jaroslav@633:      * maintained by this queue.  (In other words, this method must allocate
jaroslav@633:      * a new array).  The caller is thus free to modify the returned array.
jaroslav@633:      *
jaroslav@633:      * <p>This method acts as bridge between array-based and collection-based
jaroslav@633:      * APIs.
jaroslav@633:      *
jaroslav@633:      * @return an array containing all of the elements in this queue
jaroslav@633:      */
jaroslav@633:     public Object[] toArray() {
jaroslav@633:         return Arrays.copyOf(queue, size);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Returns an array containing all of the elements in this queue; the
jaroslav@633:      * runtime type of the returned array is that of the specified array.
jaroslav@633:      * The returned array elements are in no particular order.
jaroslav@633:      * If the queue fits in the specified array, it is returned therein.
jaroslav@633:      * Otherwise, a new array is allocated with the runtime type of the
jaroslav@633:      * specified array and the size of this queue.
jaroslav@633:      *
jaroslav@633:      * <p>If the queue fits in the specified array with room to spare
jaroslav@633:      * (i.e., the array has more elements than the queue), the element in
jaroslav@633:      * the array immediately following the end of the collection is set to
jaroslav@633:      * {@code null}.
jaroslav@633:      *
jaroslav@633:      * <p>Like the {@link #toArray()} method, this method acts as bridge between
jaroslav@633:      * array-based and collection-based APIs.  Further, this method allows
jaroslav@633:      * precise control over the runtime type of the output array, and may,
jaroslav@633:      * under certain circumstances, be used to save allocation costs.
jaroslav@633:      *
jaroslav@633:      * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
jaroslav@633:      * The following code can be used to dump the queue into a newly
jaroslav@633:      * allocated array of <tt>String</tt>:
jaroslav@633:      *
jaroslav@633:      * <pre>
jaroslav@633:      *     String[] y = x.toArray(new String[0]);</pre>
jaroslav@633:      *
jaroslav@633:      * Note that <tt>toArray(new Object[0])</tt> is identical in function to
jaroslav@633:      * <tt>toArray()</tt>.
jaroslav@633:      *
jaroslav@633:      * @param a the array into which the elements of the queue are to
jaroslav@633:      *          be stored, if it is big enough; otherwise, a new array of the
jaroslav@633:      *          same runtime type is allocated for this purpose.
jaroslav@633:      * @return an array containing all of the elements in this queue
jaroslav@633:      * @throws ArrayStoreException if the runtime type of the specified array
jaroslav@633:      *         is not a supertype of the runtime type of every element in
jaroslav@633:      *         this queue
jaroslav@633:      * @throws NullPointerException if the specified array is null
jaroslav@633:      */
jaroslav@633:     public <T> T[] toArray(T[] a) {
jaroslav@633:         if (a.length < size)
jaroslav@633:             // Make a new array of a's runtime type, but my contents:
jaroslav@633:             return (T[]) Arrays.copyOf(queue, size, a.getClass());
jaroslav@633:         System.arraycopy(queue, 0, a, 0, size);
jaroslav@633:         if (a.length > size)
jaroslav@633:             a[size] = null;
jaroslav@633:         return a;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Returns an iterator over the elements in this queue. The iterator
jaroslav@633:      * does not return the elements in any particular order.
jaroslav@633:      *
jaroslav@633:      * @return an iterator over the elements in this queue
jaroslav@633:      */
jaroslav@633:     public Iterator<E> iterator() {
jaroslav@633:         return new Itr();
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private final class Itr implements Iterator<E> {
jaroslav@633:         /**
jaroslav@633:          * Index (into queue array) of element to be returned by
jaroslav@633:          * subsequent call to next.
jaroslav@633:          */
jaroslav@633:         private int cursor = 0;
jaroslav@633: 
jaroslav@633:         /**
jaroslav@633:          * Index of element returned by most recent call to next,
jaroslav@633:          * unless that element came from the forgetMeNot list.
jaroslav@633:          * Set to -1 if element is deleted by a call to remove.
jaroslav@633:          */
jaroslav@633:         private int lastRet = -1;
jaroslav@633: 
jaroslav@633:         /**
jaroslav@633:          * A queue of elements that were moved from the unvisited portion of
jaroslav@633:          * the heap into the visited portion as a result of "unlucky" element
jaroslav@633:          * removals during the iteration.  (Unlucky element removals are those
jaroslav@633:          * that require a siftup instead of a siftdown.)  We must visit all of
jaroslav@633:          * the elements in this list to complete the iteration.  We do this
jaroslav@633:          * after we've completed the "normal" iteration.
jaroslav@633:          *
jaroslav@633:          * We expect that most iterations, even those involving removals,
jaroslav@633:          * will not need to store elements in this field.
jaroslav@633:          */
jaroslav@633:         private ArrayDeque<E> forgetMeNot = null;
jaroslav@633: 
jaroslav@633:         /**
jaroslav@633:          * Element returned by the most recent call to next iff that
jaroslav@633:          * element was drawn from the forgetMeNot list.
jaroslav@633:          */
jaroslav@633:         private E lastRetElt = null;
jaroslav@633: 
jaroslav@633:         /**
jaroslav@633:          * The modCount value that the iterator believes that the backing
jaroslav@633:          * Queue should have.  If this expectation is violated, the iterator
jaroslav@633:          * has detected concurrent modification.
jaroslav@633:          */
jaroslav@633:         private int expectedModCount = modCount;
jaroslav@633: 
jaroslav@633:         public boolean hasNext() {
jaroslav@633:             return cursor < size ||
jaroslav@633:                 (forgetMeNot != null && !forgetMeNot.isEmpty());
jaroslav@633:         }
jaroslav@633: 
jaroslav@633:         public E next() {
jaroslav@633:             if (expectedModCount != modCount)
jaroslav@633:                 throw new ConcurrentModificationException();
jaroslav@633:             if (cursor < size)
jaroslav@633:                 return (E) queue[lastRet = cursor++];
jaroslav@633:             if (forgetMeNot != null) {
jaroslav@633:                 lastRet = -1;
jaroslav@633:                 lastRetElt = forgetMeNot.poll();
jaroslav@633:                 if (lastRetElt != null)
jaroslav@633:                     return lastRetElt;
jaroslav@633:             }
jaroslav@633:             throw new NoSuchElementException();
jaroslav@633:         }
jaroslav@633: 
jaroslav@633:         public void remove() {
jaroslav@633:             if (expectedModCount != modCount)
jaroslav@633:                 throw new ConcurrentModificationException();
jaroslav@633:             if (lastRet != -1) {
jaroslav@633:                 E moved = PriorityQueue.this.removeAt(lastRet);
jaroslav@633:                 lastRet = -1;
jaroslav@633:                 if (moved == null)
jaroslav@633:                     cursor--;
jaroslav@633:                 else {
jaroslav@633:                     if (forgetMeNot == null)
jaroslav@633:                         forgetMeNot = new ArrayDeque<>();
jaroslav@633:                     forgetMeNot.add(moved);
jaroslav@633:                 }
jaroslav@633:             } else if (lastRetElt != null) {
jaroslav@633:                 PriorityQueue.this.removeEq(lastRetElt);
jaroslav@633:                 lastRetElt = null;
jaroslav@633:             } else {
jaroslav@633:                 throw new IllegalStateException();
jaroslav@633:             }
jaroslav@633:             expectedModCount = modCount;
jaroslav@633:         }
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     public int size() {
jaroslav@633:         return size;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Removes all of the elements from this priority queue.
jaroslav@633:      * The queue will be empty after this call returns.
jaroslav@633:      */
jaroslav@633:     public void clear() {
jaroslav@633:         modCount++;
jaroslav@633:         for (int i = 0; i < size; i++)
jaroslav@633:             queue[i] = null;
jaroslav@633:         size = 0;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     public E poll() {
jaroslav@633:         if (size == 0)
jaroslav@633:             return null;
jaroslav@633:         int s = --size;
jaroslav@633:         modCount++;
jaroslav@633:         E result = (E) queue[0];
jaroslav@633:         E x = (E) queue[s];
jaroslav@633:         queue[s] = null;
jaroslav@633:         if (s != 0)
jaroslav@633:             siftDown(0, x);
jaroslav@633:         return result;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Removes the ith element from queue.
jaroslav@633:      *
jaroslav@633:      * Normally this method leaves the elements at up to i-1,
jaroslav@633:      * inclusive, untouched.  Under these circumstances, it returns
jaroslav@633:      * null.  Occasionally, in order to maintain the heap invariant,
jaroslav@633:      * it must swap a later element of the list with one earlier than
jaroslav@633:      * i.  Under these circumstances, this method returns the element
jaroslav@633:      * that was previously at the end of the list and is now at some
jaroslav@633:      * position before i. This fact is used by iterator.remove so as to
jaroslav@633:      * avoid missing traversing elements.
jaroslav@633:      */
jaroslav@633:     private E removeAt(int i) {
jaroslav@633:         assert i >= 0 && i < size;
jaroslav@633:         modCount++;
jaroslav@633:         int s = --size;
jaroslav@633:         if (s == i) // removed last element
jaroslav@633:             queue[i] = null;
jaroslav@633:         else {
jaroslav@633:             E moved = (E) queue[s];
jaroslav@633:             queue[s] = null;
jaroslav@633:             siftDown(i, moved);
jaroslav@633:             if (queue[i] == moved) {
jaroslav@633:                 siftUp(i, moved);
jaroslav@633:                 if (queue[i] != moved)
jaroslav@633:                     return moved;
jaroslav@633:             }
jaroslav@633:         }
jaroslav@633:         return null;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Inserts item x at position k, maintaining heap invariant by
jaroslav@633:      * promoting x up the tree until it is greater than or equal to
jaroslav@633:      * its parent, or is the root.
jaroslav@633:      *
jaroslav@633:      * To simplify and speed up coercions and comparisons. the
jaroslav@633:      * Comparable and Comparator versions are separated into different
jaroslav@633:      * methods that are otherwise identical. (Similarly for siftDown.)
jaroslav@633:      *
jaroslav@633:      * @param k the position to fill
jaroslav@633:      * @param x the item to insert
jaroslav@633:      */
jaroslav@633:     private void siftUp(int k, E x) {
jaroslav@633:         if (comparator != null)
jaroslav@633:             siftUpUsingComparator(k, x);
jaroslav@633:         else
jaroslav@633:             siftUpComparable(k, x);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private void siftUpComparable(int k, E x) {
jaroslav@633:         Comparable<? super E> key = (Comparable<? super E>) x;
jaroslav@633:         while (k > 0) {
jaroslav@633:             int parent = (k - 1) >>> 1;
jaroslav@633:             Object e = queue[parent];
jaroslav@633:             if (key.compareTo((E) e) >= 0)
jaroslav@633:                 break;
jaroslav@633:             queue[k] = e;
jaroslav@633:             k = parent;
jaroslav@633:         }
jaroslav@633:         queue[k] = key;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private void siftUpUsingComparator(int k, E x) {
jaroslav@633:         while (k > 0) {
jaroslav@633:             int parent = (k - 1) >>> 1;
jaroslav@633:             Object e = queue[parent];
jaroslav@633:             if (comparator.compare(x, (E) e) >= 0)
jaroslav@633:                 break;
jaroslav@633:             queue[k] = e;
jaroslav@633:             k = parent;
jaroslav@633:         }
jaroslav@633:         queue[k] = x;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Inserts item x at position k, maintaining heap invariant by
jaroslav@633:      * demoting x down the tree repeatedly until it is less than or
jaroslav@633:      * equal to its children or is a leaf.
jaroslav@633:      *
jaroslav@633:      * @param k the position to fill
jaroslav@633:      * @param x the item to insert
jaroslav@633:      */
jaroslav@633:     private void siftDown(int k, E x) {
jaroslav@633:         if (comparator != null)
jaroslav@633:             siftDownUsingComparator(k, x);
jaroslav@633:         else
jaroslav@633:             siftDownComparable(k, x);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private void siftDownComparable(int k, E x) {
jaroslav@633:         Comparable<? super E> key = (Comparable<? super E>)x;
jaroslav@633:         int half = size >>> 1;        // loop while a non-leaf
jaroslav@633:         while (k < half) {
jaroslav@633:             int child = (k << 1) + 1; // assume left child is least
jaroslav@633:             Object c = queue[child];
jaroslav@633:             int right = child + 1;
jaroslav@633:             if (right < size &&
jaroslav@633:                 ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
jaroslav@633:                 c = queue[child = right];
jaroslav@633:             if (key.compareTo((E) c) <= 0)
jaroslav@633:                 break;
jaroslav@633:             queue[k] = c;
jaroslav@633:             k = child;
jaroslav@633:         }
jaroslav@633:         queue[k] = key;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     private void siftDownUsingComparator(int k, E x) {
jaroslav@633:         int half = size >>> 1;
jaroslav@633:         while (k < half) {
jaroslav@633:             int child = (k << 1) + 1;
jaroslav@633:             Object c = queue[child];
jaroslav@633:             int right = child + 1;
jaroslav@633:             if (right < size &&
jaroslav@633:                 comparator.compare((E) c, (E) queue[right]) > 0)
jaroslav@633:                 c = queue[child = right];
jaroslav@633:             if (comparator.compare(x, (E) c) <= 0)
jaroslav@633:                 break;
jaroslav@633:             queue[k] = c;
jaroslav@633:             k = child;
jaroslav@633:         }
jaroslav@633:         queue[k] = x;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Establishes the heap invariant (described above) in the entire tree,
jaroslav@633:      * assuming nothing about the order of the elements prior to the call.
jaroslav@633:      */
jaroslav@633:     private void heapify() {
jaroslav@633:         for (int i = (size >>> 1) - 1; i >= 0; i--)
jaroslav@633:             siftDown(i, (E) queue[i]);
jaroslav@633:     }
jaroslav@633: 
jaroslav@633:     /**
jaroslav@633:      * Returns the comparator used to order the elements in this
jaroslav@633:      * queue, or {@code null} if this queue is sorted according to
jaroslav@633:      * the {@linkplain Comparable natural ordering} of its elements.
jaroslav@633:      *
jaroslav@633:      * @return the comparator used to order this queue, or
jaroslav@633:      *         {@code null} if this queue is sorted according to the
jaroslav@633:      *         natural ordering of its elements
jaroslav@633:      */
jaroslav@633:     public Comparator<? super E> comparator() {
jaroslav@633:         return comparator;
jaroslav@633:     }
jaroslav@633: 
jaroslav@633: 
jaroslav@633: }