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package java.util; |
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/** |
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* A priority queue based on a priority heap. This queue orders |
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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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* 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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* according to a {@link java.util.Comparator}, depending on which |
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* 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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* <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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* <tt>null</tt> elements. |
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* |
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* <p>A priority queue has a <i>capacity</i>. The capacity is the |
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* size of the array used internally to store the elements on the |
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* queue, and is limited to <tt>Integer.MAX_VALUE-1</tt>. |
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* queue. |
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* It is always at least as large as the queue size. As |
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* elements are added to a priority queue, its capacity grows |
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* automatically. The details of the growth policy are not specified. |
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* |
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* <p>The 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.BlockingPriorityQueue} 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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* @author Josh Bloch |
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*/ |
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public class PriorityQueue<E> extends AbstractQueue<E> |
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implements Sorted, Queue<E>, java.io.Serializable { |
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implements Queue<E>, java.io.Serializable { |
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private static final long serialVersionUID = -7720805057305804111L; |
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private static final int DEFAULT_INITIAL_CAPACITY = 11; |
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private transient int modCount = 0; |
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/** |
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* Create a <tt>PriorityQueue</tt> with the default initial capacity |
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* 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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* 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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* Create a <tt>PriorityQueue</tt> with the specified initial capacity |
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* Creates a <tt>PriorityQueue</tt> with the specified initial capacity |
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* that orders its elements according to their natural ordering |
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* (using <tt>Comparable</tt>.) |
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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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* Create a <tt>PriorityQueue</tt> with the specified initial capacity |
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* Creates a <tt>PriorityQueue</tt> with the specified initial capacity |
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* that orders its elements according to the specified comparator. |
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* |
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* @param initialCapacity the initial capacity for this priority queue. |
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* @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, Comparator<? super E> comparator) { |
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public PriorityQueue(int initialCapacity, |
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Comparator<? super E> comparator) { |
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if (initialCapacity < 1) |
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throw new IllegalArgumentException(); |
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this.queue = new Object[initialCapacity + 1]; |
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} |
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|
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/** |
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* Create a <tt>PriorityQueue</tt> containing the elements in the specified |
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* collection. The priority queue has an initial capacity of 110% of the |
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* size of the specified collection (bounded by |
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* <tt>Integer.MAX_VALUE-1</tt>); or 1 if the collection is empty. |
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* If the specified collection |
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* implements the {@link Sorted} interface, the priority queue will be |
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* sorted according to the same comparator, or according to its elements' |
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* natural order if the collection is sorted according to its elements' |
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* natural order. If the specified collection does not implement |
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* <tt>Sorted</tt>, the priority queue is ordered according to |
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* its elements' natural order. |
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* |
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* @param c the collection whose elements are to be placed |
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* into this priority queue. |
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* @throws ClassCastException if elements of the specified collection |
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* cannot be compared to one another according to the priority |
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* queue's ordering. |
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* @throws NullPointerException if <tt>c</tt> or any element within it |
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* is <tt>null</tt> |
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* Common code to initialize underlying queue array across |
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* constructors below. |
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*/ |
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public PriorityQueue(Collection<? extends E> c) { |
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private void initializeArray(Collection<? extends E> c) { |
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int sz = c.size(); |
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int initialCapacity = (int)Math.min((sz * 110L) / 100, |
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Integer.MAX_VALUE - 1); |
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initialCapacity = 1; |
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this.queue = new Object[initialCapacity + 1]; |
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} |
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|
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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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*/ |
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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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// FIXME: if c is larger than Integer.MAX_VALUE we'll |
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// overflow the array |
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if (c instanceof Sorted) { |
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comparator = ((Sorted)c).comparator(); |
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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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*/ |
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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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} |
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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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for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) |
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add(i.next()); |
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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; |
259 |
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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(); |
263 |
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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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// Queue Methods |
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|
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|
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|
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/** |
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* Add the specified element to this priority queue. |
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* |
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++size; |
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|
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// Grow backing store if necessary |
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// FIXME: watch for overflow |
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// FIXME: what if we're full? |
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while (size >= queue.length) { |
182 |
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Object[] newQueue = new Object[2 * queue.length]; |
183 |
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System.arraycopy(queue, 0, newQueue, 0, queue.length); |
184 |
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queue = newQueue; |
185 |
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} |
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if (size >= queue.length) |
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> |
grow(size); |
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|
297 |
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queue[size] = o; |
298 |
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fixUp(size); |
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return (E) queue[1]; |
310 |
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} |
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|
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// Collection Methods |
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|
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// these first two override just to get the throws docs |
312 |
> |
// Collection Methods - the first two override to update docs |
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|
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/** |
315 |
< |
* @throws NullPointerException if the specified element is <tt>null</tt>. |
315 |
> |
* Adds the specified element to this queue. |
316 |
> |
* @return <tt>true</tt> (as per the general contract of |
317 |
> |
* <tt>Collection.add</tt>). |
318 |
> |
* |
319 |
> |
* @throws NullPointerException {@inheritDoc} |
320 |
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* @throws ClassCastException if the specified element cannot be compared |
321 |
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* with elements currently in the priority queue according |
322 |
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* to the priority queue's ordering. |
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return super.add(o); |
326 |
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} |
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|
328 |
+ |
|
329 |
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/** |
330 |
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* Adds all of the elements in the specified collection to this queue. |
331 |
+ |
* The behavior of this operation is undefined if |
332 |
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* the specified collection is modified while the operation is in |
333 |
+ |
* progress. (This implies that the behavior of this call is undefined if |
334 |
+ |
* the specified collection is this queue, and this queue is nonempty.) |
335 |
+ |
* <p> |
336 |
+ |
* This implementation iterates over the specified collection, and adds |
337 |
+ |
* each object returned by the iterator to this collection, in turn. |
338 |
+ |
* @throws NullPointerException {@inheritDoc} |
339 |
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* @throws ClassCastException if any element cannot be compared |
340 |
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* with elements currently in the priority queue according |
341 |
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* to the priority queue's ordering. |
220 |
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* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt> |
221 |
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* is <tt>null</tt> |
342 |
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*/ |
343 |
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public boolean addAll(Collection<? extends E> c) { |
344 |
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return super.addAll(c); |
345 |
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} |
346 |
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|
347 |
+ |
|
348 |
+ |
/** |
349 |
+ |
* Removes a single instance of the specified element from this |
350 |
+ |
* queue, if it is present. More formally, |
351 |
+ |
* removes an element <tt>e</tt> such that <tt>(o==null ? e==null : |
352 |
+ |
* o.equals(e))</tt>, if the queue contains one or more such |
353 |
+ |
* elements. Returns <tt>true</tt> if the queue contained the |
354 |
+ |
* specified element (or equivalently, if the queue changed as a |
355 |
+ |
* result of the call). |
356 |
+ |
* |
357 |
+ |
* <p>This implementation iterates over the queue looking for the |
358 |
+ |
* specified element. If it finds the element, it removes the element |
359 |
+ |
* from the queue using the iterator's remove method.<p> |
360 |
+ |
* |
361 |
+ |
*/ |
362 |
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public boolean remove(Object o) { |
363 |
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if (o == null) |
364 |
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return false; |
381 |
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return false; |
382 |
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} |
383 |
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|
384 |
+ |
/** |
385 |
+ |
* Returns an iterator over the elements in this queue. The iterator |
386 |
+ |
* does not return the elements in any particular order. |
387 |
+ |
* |
388 |
+ |
* @return an iterator over the elements in this queue. |
389 |
+ |
*/ |
390 |
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public Iterator<E> iterator() { |
391 |
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return new Itr(); |
392 |
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} |
431 |
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checkForComodification(); |
432 |
|
|
433 |
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PriorityQueue.this.remove(lastRet); |
434 |
< |
if (lastRet < cursor) |
294 |
< |
cursor--; |
434 |
> |
cursor--; |
435 |
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lastRet = 0; |
436 |
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expectedModCount = modCount; |
437 |
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} |
442 |
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} |
443 |
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} |
444 |
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|
305 |
– |
/** |
306 |
– |
* Returns the number of elements in this priority queue. |
307 |
– |
* |
308 |
– |
* @return the number of elements in this priority queue. |
309 |
– |
*/ |
445 |
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public int size() { |
446 |
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return size; |
447 |
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} |
463 |
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* Removes and returns the ith element from queue. Recall |
464 |
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* that queue is one-based, so 1 <= i <= size. |
465 |
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* |
331 |
– |
* XXX: Could further special-case i==size, but is it worth it? |
332 |
– |
* XXX: Could special-case i==0, but is it worth it? |
466 |
|
*/ |
467 |
|
private E remove(int i) { |
468 |
|
assert i <= size; |
517 |
|
private void fixDown(int k) { |
518 |
|
int j; |
519 |
|
if (comparator == null) { |
520 |
< |
while ((j = k << 1) <= size) { |
520 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
521 |
|
if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
522 |
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j++; // j indexes smallest kid |
523 |
|
if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0) |
526 |
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k = j; |
527 |
|
} |
528 |
|
} else { |
529 |
< |
while ((j = k << 1) <= size) { |
529 |
> |
while ((j = k << 1) <= size && (j > 0)) { |
530 |
|
if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
531 |
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j++; // j indexes smallest kid |
532 |
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if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) |
537 |
|
} |
538 |
|
} |
539 |
|
|
540 |
+ |
|
541 |
+ |
/** |
542 |
+ |
* Returns the comparator used to order this collection, or <tt>null</tt> |
543 |
+ |
* if this collection is sorted according to its elements natural ordering |
544 |
+ |
* (using <tt>Comparable</tt>). |
545 |
+ |
* |
546 |
+ |
* @return the comparator used to order this collection, or <tt>null</tt> |
547 |
+ |
* if this collection is sorted according to its elements natural ordering. |
548 |
+ |
*/ |
549 |
|
public Comparator<? super E> comparator() { |
550 |
|
return comparator; |
551 |
|
} |
559 |
|
* <tt>Object</tt>) in the proper order. |
560 |
|
* @param s the stream |
561 |
|
*/ |
562 |
< |
private synchronized void writeObject(java.io.ObjectOutputStream s) |
562 |
> |
private void writeObject(java.io.ObjectOutputStream s) |
563 |
|
throws java.io.IOException{ |
564 |
|
// Write out element count, and any hidden stuff |
565 |
|
s.defaultWriteObject(); |
577 |
|
* deserialize it). |
578 |
|
* @param s the stream |
579 |
|
*/ |
580 |
< |
private synchronized void readObject(java.io.ObjectInputStream s) |
580 |
> |
private void readObject(java.io.ObjectInputStream s) |
581 |
|
throws java.io.IOException, ClassNotFoundException { |
582 |
|
// Read in size, and any hidden stuff |
583 |
|
s.defaultReadObject(); |