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package java.util; |
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/** |
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* An unbounded 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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* {@link java.util.TreeMap}: elements are ordered |
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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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public class PriorityQueue<E> extends AbstractQueue<E> |
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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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/** |
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/** |
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* Creates a <tt>PriorityQueue</tt> with the default initial capacity |
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* (11) that orders its elements according to their natural |
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* ordering (using <tt>Comparable</tt>.) |
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* 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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* 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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* @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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* 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 SortedSet} or is another |
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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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*/ |
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public PriorityQueue(Collection<? extends E> c) { |
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initializeArray(c); |
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if (c instanceof SortedSet<? extends E>) { |
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SortedSet<? extends E> s = (SortedSet<? extends E>) 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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} |
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else if (c instanceof PriorityQueue<? extends E>) { |
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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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} |
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else { |
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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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// Queue Methods |
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/** |
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* Add the specified element to this priority queue. |
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* |
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return (E) queue[1]; |
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} |
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// Collection Methods |
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// these first two override just to get the throws docs |
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// Collection Methods - the first two override to update docs |
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/** |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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* Adds the specified element to this queue. |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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* |
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* @throws NullPointerException {@inheritDoc} |
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* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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return super.add(o); |
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} |
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/** |
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* Adds all of the elements in the specified collection to this queue. |
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* The behavior of this operation is undefined if |
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* the specified collection is modified while the operation is in |
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* progress. (This implies that the behavior of this call is undefined if |
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* the specified collection is this queue, and this queue is nonempty.) |
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* <p> |
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* This implementation iterates over the specified collection, and adds |
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* each object returned by the iterator to this collection, in turn. |
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* @throws NullPointerException {@inheritDoc} |
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* @throws ClassCastException if any element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt> |
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* is <tt>null</tt> |
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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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return super.addAll(c); |
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} |
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/** |
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* 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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* o.equals(e))</tt>, if the queue contains one or more such |
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* elements. Returns <tt>true</tt> if the queue contained the |
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* specified element (or equivalently, if the queue changed as a |
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* result of the call). |
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* |
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* <p>This implementation iterates over the queue looking for the |
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* specified element. If it finds the element, it removes the element |
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* from the queue using the iterator's remove method.<p> |
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* |
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*/ |
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public boolean remove(Object o) { |
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if (o == null) |
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return false; |
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return false; |
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} |
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/** |
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* Returns an iterator over the elements in this queue. The iterator |
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* does not return the elements in any particular order. |
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* |
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* @return an iterator over the elements in this queue. |
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*/ |
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public Iterator<E> iterator() { |
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return new Itr(); |
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} |
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checkForComodification(); |
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PriorityQueue.this.remove(lastRet); |
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if (lastRet < cursor) |
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cursor--; |
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cursor--; |
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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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/** |
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* Returns the number of elements in this priority queue. |
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* |
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* @return the number of elements in this priority queue. |
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*/ |
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public int size() { |
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return size; |
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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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* |
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* XXX: Could further special-case i==size, but is it worth it? |
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* XXX: Could special-case i==0, but is it worth it? |
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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 void fixDown(int k) { |
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int j; |
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if (comparator == null) { |
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while ((j = k << 1) <= size) { |
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while ((j = k << 1) <= size && j > 0) { |
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if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0) |
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j++; // j indexes smallest kid |
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if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0) |
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k = j; |
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} |
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} else { |
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while ((j = k << 1) <= size) { |
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while ((j = k << 1) <= size && j > 0) { |
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if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) |
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j++; // j indexes smallest kid |
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if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) |
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} |
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} |
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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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* if this collection is sorted according to its elements natural ordering |
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* (using <tt>Comparable</tt>). |
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* |
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* @return the comparator used to order this collection, or <tt>null</tt> |
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* if this collection is sorted according to its elements natural ordering. |
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*/ |
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public Comparator<? super E> comparator() { |
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return comparator; |
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} |