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package java.util; |
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/* |
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* %W% %E% |
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* |
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* Copyright 2003 Sun Microsystems, Inc. All rights reserved. |
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* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. |
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*/ |
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package java.util; |
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/** |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* This queue orders |
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* elements according to an order specified at construction time, which is |
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* specified in the same manner as {@link java.util.TreeSet} and |
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* {@link java.util.TreeMap}: elements are ordered |
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* either according to their <i>natural order</i> (see {@link Comparable}), or |
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* according to a {@link java.util.Comparator}, depending on which |
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* constructor is used. |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* This queue orders elements according to an order specified at construction |
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* time, which is specified in the same manner as {@link java.util.TreeSet} |
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* and {@link java.util.TreeMap}: elements are ordered either according to |
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* their <i>natural order</i> (see {@link Comparable}), or according to a |
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* {@link java.util.Comparator}, depending on which constructor is used. |
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* <p>The <em>head</em> of this queue is the <em>least</em> element with |
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* respect to the specified ordering. |
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* If multiple elements are tied for least value, the |
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* head is one of those elements. A priority queue does not permit |
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* respect to the specified ordering. If multiple elements are tied for least |
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* value, the head is one of those elements. A priority queue does not permit |
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* <tt>null</tt> elements. |
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* |
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* <p>The {@link #remove()} and {@link #poll()} methods remove and |
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* <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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/** |
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* Initially fill elements of the queue array under the |
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* knowledge that it is sorted or is another PQ, in which |
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* case we can just place the elements without fixups. |
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* case we can just place the elements in the order presented. |
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*/ |
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private void fillFromSorted(Collection<? extends E> c) { |
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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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queue[++size] = i.next(); |
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} |
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/** |
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* Initially fill elements of the queue array that is |
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* not to our knowledge sorted, so we must add them |
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* one by one. |
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* Initially fill elements of the queue array that is not to our knowledge |
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* sorted, so we must rearrange the elements to guarantee the heap |
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* invariant. |
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*/ |
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private void fillFromUnsorted(Collection<? extends E> c) { |
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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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add(i.next()); |
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queue[++size] = i.next(); |
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heapify(); |
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} |
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/** |
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queue = newQueue; |
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} |
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// Queue Methods |
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// Queue Methods |
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/** |
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* Add the specified element to this priority queue. |
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public E poll() { |
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if (size == 0) |
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return null; |
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return (E) remove(1); |
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return remove(); |
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} |
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public E peek() { |
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} |
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/** |
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/** |
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* Removes a single instance of the specified element from this |
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* queue, if it is present. More formally, |
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* removes an element <tt>e</tt> such that <tt>(o==null ? e==null : |
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if (comparator == null) { |
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for (int i = 1; i <= size; i++) { |
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if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) { |
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remove(i); |
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removeAt(i); |
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return true; |
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} |
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} |
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} else { |
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for (int i = 1; i <= size; i++) { |
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if (comparator.compare((E)queue[i], (E)o) == 0) { |
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remove(i); |
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removeAt(i); |
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return true; |
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} |
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} |
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private int cursor = 1; |
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/** |
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* Index of element returned by most recent call to next or |
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* previous. Reset to 0 if this element is deleted by a call |
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* to remove. |
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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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private int expectedModCount = modCount; |
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// Workarounds until version that better handles remove() installed. |
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// These are used to copy-on-write the array upon first remove |
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private Object[] q = queue; |
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private int qsize = size; |
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/** |
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* A list of elements that were moved from the unvisited portion of |
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* the heap into the visited portion as a result of "unlucky" element |
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* removals during the iteration. (Unlucky element removals are those |
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* that require a fixup instead of a fixdown.) We must visit all of |
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* the elements in this list to complete the iteration. We do this |
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* after we've completed the "normal" iteration. |
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* |
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* We expect that most iterations, even those involving removals, |
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* will not use need to store elements in this field. |
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*/ |
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private ArrayList<E> forgetMeNot = null; |
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/** |
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* Element returned by the most recent call to next iff that |
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* element was drawn from the forgetMeNot list. |
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*/ |
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private Object lastRetElt = null; |
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public boolean hasNext() { |
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return cursor <= qsize; |
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return cursor <= size || forgetMeNot != null; |
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} |
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public E next() { |
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checkForComodification(); |
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if (cursor > qsize) |
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E result; |
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if (cursor <= size) { |
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result = (E) queue[cursor]; |
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lastRet = cursor++; |
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} |
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else if (forgetMeNot == null) |
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throw new NoSuchElementException(); |
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E result = (E) q[cursor]; |
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lastRet = cursor++; |
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else { |
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int remaining = forgetMeNot.size(); |
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result = forgetMeNot.remove(remaining - 1); |
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if (remaining == 1) |
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forgetMeNot = null; |
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lastRet = 0; |
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lastRetElt = result; |
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} |
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return result; |
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} |
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public void remove() { |
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if (lastRet == 0) |
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throw new IllegalStateException(); |
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checkForComodification(); |
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// Copy on first remove |
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if (q == queue) { |
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q = new Object[queue.length]; |
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System.arraycopy(queue, 0, q, 0, queue.length); |
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if (lastRet != 0) { |
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E moved = PriorityQueue.this.removeAt(lastRet); |
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lastRet = 0; |
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if (moved == null) { |
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cursor--; |
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} else { |
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if (forgetMeNot == null) |
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forgetMeNot = new ArrayList<E>(); |
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forgetMeNot.add(moved); |
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} |
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} else if (lastRetElt != null) { |
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PriorityQueue.this.remove(lastRetElt); |
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lastRetElt = null; |
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} else { |
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throw new IllegalStateException(); |
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} |
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PriorityQueue.this.remove(q[lastRet]); |
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lastRet = 0; |
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expectedModCount = modCount; |
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} |
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} |
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/** |
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* Removes and returns the ith element from queue. Recall |
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* that queue is one-based, so 1 <= i <= size. |
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* Removes and returns the first element from queue. |
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*/ |
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public E remove() { |
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if (size == 0) |
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throw new NoSuchElementException(); |
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modCount++; |
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E result = (E) queue[1]; |
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queue[1] = queue[size]; |
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queue[size--] = null; // Drop extra ref to prevent memory leak |
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if (size > 1) |
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fixDown(1); |
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return result; |
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} |
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/** |
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* Removes and returns the ith element from queue. (Recall that queue |
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* is one-based, so 1 <= i <= size.) |
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* |
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* Normally this method leaves the elements at positions from 1 up to i-1, |
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* inclusive, untouched. Under these circumstances, it returns null. |
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* Occasionally, in order to maintain the heap invariant, it must move |
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* the last element of the list to some index in the range [2, i-1], |
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* and move the element previously at position (i/2) to position i. |
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* Under these circumstances, this method returns the element that was |
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* previously at the end of the list and is now at some position between |
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* 2 and i-1 inclusive. |
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*/ |
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private E remove(int i) { |
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assert i <= size; |
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private E removeAt(int i) { |
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assert i > 0 && i <= size; |
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modCount++; |
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E result = (E) queue[i]; |
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queue[i] = queue[size]; |
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E moved = (E) queue[size]; |
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queue[i] = moved; |
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queue[size--] = null; // Drop extra ref to prevent memory leak |
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if (i <= size) { |
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fixDown(i); |
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fixUp(i); |
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if (queue[i] == moved) { |
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fixUp(i); |
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if (queue[i] != moved) |
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return moved; |
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} |
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} |
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return result; |
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return null; |
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} |
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/** |
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k = j; |
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} |
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} |
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} |
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/** |
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* Establishes the heap invariant (described above) in the entire tree, |
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* assuming nothing about the order of the elements prior to the call. |
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*/ |
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private void heapify() { |
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for (int i = size/2; i >= 1; i--) |
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fixDown(i); |
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} |
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/** |
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* Returns the comparator used to order this collection, or <tt>null</tt> |
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// Read in all elements in the proper order. |
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for (int i=0; i<size; i++) |
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queue[i] = s.readObject(); |
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queue[i] = (E) s.readObject(); |
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} |
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} |
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