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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.1 by tim, Wed May 14 21:30:45 2003 UTC vs.
Revision 1.35 by dl, Wed Aug 27 10:27:07 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
2	<
3	<	import java.util.*;
1	>	package java.util;
2
3		/**
4	<	* An unbounded (resizable) priority queue based on a priority
5	<	* heap.The take operation returns the least element with respect to
6	<	* the given ordering. (If more than one element is tied for least
7	<	* value, one of them is arbitrarily chosen to be returned -- no
8	<	* guarantees are made for ordering across ties.) Ordering follows the
9	<	* java.util.Collection conventions: Either the elements must be
10	<	* Comparable, or a Comparator must be supplied. Comparison failures
11	<	* throw ClassCastExceptions during insertions and extractions.
12	<	**/
13	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
14	<	public PriorityQueue(int initialCapacity) {}
15	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
4	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
5	>	* This queue orders
6	>	* elements according to an order specified at construction time, which is
7	>	* specified in the same manner as {@link java.util.TreeSet} and
8	>	* {@link java.util.TreeMap}: elements are ordered
9	>	* either according to their <i>natural order</i> (see {@link Comparable}), or
10	>	* according to a {@link java.util.Comparator}, depending on which
11	>	* constructor is used.
12	>	* <p>The <em>head</em> of this queue is the <em>least</em> element with
13	>	* respect to the specified ordering.
14	>	* If multiple elements are tied for least value, the
15	>	* head is one of those elements. A priority queue does not permit
16	>	* <tt>null</tt> elements.
17	>	*
18	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
19	>	* return the head of the queue.
20	>	*
21	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
22	>	* not delete, the head of the queue.
23	>	*
24	>	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
25	>	* size of the array used internally to store the elements on the
26	>	* queue.
27	>	* It is always at least as large as the queue size.  As
28	>	* elements are added to a priority queue, its capacity grows
29	>	* automatically.  The details of the growth policy are not specified.
30	>	*
31	>	* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
32	>	* guaranteed to traverse the elements of the PriorityQueue in any
33	>	* particular order. If you need ordered traversal, consider using
34	>	* <tt>Arrays.sort(pq.toArray())</tt>.
35	>	*
36	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
37	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
38	>	* instance concurrently if any of the threads modifies the list
39	>	* structurally. Instead, use the thread-safe {@link
40	>	* java.util.concurrent.PriorityBlockingQueue} class.
41	>	*
42	>	*
43	>	* <p>Implementation note: this implementation provides O(log(n)) time
44	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
45	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
46	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
47	>	* constant time for the retrieval methods (<tt>peek</tt>,
48	>	* <tt>element</tt>, and <tt>size</tt>).
49	>	*
50	>	* <p>This class is a member of the
51	>	* <a href="{@docRoot}/../guide/collections/index.html">
52	>	* Java Collections Framework</a>.
53	>	* @since 1.5
54	>	* @author Josh Bloch
55	>	*/
56	>	public class PriorityQueue<E> extends AbstractQueue<E>
57	>	implements Queue<E>, java.io.Serializable {
58
59	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
59	>	private static final long serialVersionUID = -7720805057305804111L;
60
61	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
61	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
62
63	<	public boolean add(E x) {
64	<	return false;
63	>	/**
64	>	* Priority queue represented as a balanced binary heap: the two children
65	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
66	>	* ordered by comparator, or by the elements' natural ordering, if
67	>	* comparator is null:  For each node n in the heap and each descendant d
68	>	* of n, n <= d.
69	>	*
70	>	* The element with the lowest value is in queue[1], assuming the queue is
71	>	* nonempty.  (A one-based array is used in preference to the traditional
72	>	* zero-based array to simplify parent and child calculations.)
73	>	*
74	>	* queue.length must be >= 2, even if size == 0.
75	>	*/
76	>	private transient Object[] queue;
77	>
78	>	/**
79	>	* The number of elements in the priority queue.
80	>	*/
81	>	private int size = 0;
82	>
83	>	/**
84	>	* The comparator, or null if priority queue uses elements'
85	>	* natural ordering.
86	>	*/
87	>	private final Comparator<? super E> comparator;
88	>
89	>	/**
90	>	* The number of times this priority queue has been
91	>	* <i>structurally modified</i>.  See AbstractList for gory details.
92	>	*/
93	>	private transient int modCount = 0;
94	>
95	>	/**
96	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
97	>	* (11) that orders its elements according to their natural
98	>	* ordering (using <tt>Comparable</tt>).
99	>	*/
100	>	public PriorityQueue() {
101	>	this(DEFAULT_INITIAL_CAPACITY, null);
102		}
103	<	public boolean offer(E x) {
104	<	return false;
103	>
104	>	/**
105	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
106	>	* that orders its elements according to their natural ordering
107	>	* (using <tt>Comparable</tt>).
108	>	*
109	>	* @param initialCapacity the initial capacity for this priority queue.
110	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
111	>	* than 1
112	>	*/
113	>	public PriorityQueue(int initialCapacity) {
114	>	this(initialCapacity, null);
115		}
116	<	public boolean remove(Object x) {
117	<	return false;
116	>
117	>	/**
118	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
119	>	* that orders its elements according to the specified comparator.
120	>	*
121	>	* @param initialCapacity the initial capacity for this priority queue.
122	>	* @param comparator the comparator used to order this priority queue.
123	>	* If <tt>null</tt> then the order depends on the elements' natural
124	>	* ordering.
125	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
126	>	* than 1
127	>	*/
128	>	public PriorityQueue(int initialCapacity,
129	>	Comparator<? super E> comparator) {
130	>	if (initialCapacity < 1)
131	>	throw new IllegalArgumentException();
132	>	this.queue = new Object[initialCapacity + 1];
133	>	this.comparator = comparator;
134		}
135
136	<	public E remove() {
137	<	return null;
136	>	/**
137	>	* Common code to initialize underlying queue array across
138	>	* constructors below.
139	>	*/
140	>	private void initializeArray(Collection<? extends E> c) {
141	>	int sz = c.size();
142	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
143	>	Integer.MAX_VALUE - 1);
144	>	if (initialCapacity < 1)
145	>	initialCapacity = 1;
146	>
147	>	this.queue = new Object[initialCapacity + 1];
148		}
149	<	public Iterator<E> iterator() {
150	<	return null;
149	>
150	>	/**
151	>	* Initially fill elements of the queue array under the
152	>	* knowledge that it is sorted or is another PQ, in which
153	>	* case we can just place the elements without fixups.
154	>	*/
155	>	private void fillFromSorted(Collection<? extends E> c) {
156	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
157	>	queue[++size] = i.next();
158	>	}
159	>
160	>
161	>	/**
162	>	* Initially fill elements of the queue array that is
163	>	* not to our knowledge sorted, so we must add them
164	>	* one by one.
165	>	*/
166	>	private void fillFromUnsorted(Collection<? extends E> c) {
167	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
168	>	add(i.next());
169	>	}
170	>
171	>	/**
172	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
173	>	* specified collection.  The priority queue has an initial
174	>	* capacity of 110% of the size of the specified collection or 1
175	>	* if the collection is empty.  If the specified collection is an
176	>	* instance of a {@link java.util.SortedSet} or is another
177	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
178	>	* according to the same comparator, or according to its elements'
179	>	* natural order if the collection is sorted according to its
180	>	* elements' natural order.  Otherwise, the priority queue is
181	>	* ordered according to its elements' natural order.
182	>	*
183	>	* @param c the collection whose elements are to be placed
184	>	*        into this priority queue.
185	>	* @throws ClassCastException if elements of the specified collection
186	>	*         cannot be compared to one another according to the priority
187	>	*         queue's ordering.
188	>	* @throws NullPointerException if <tt>c</tt> or any element within it
189	>	* is <tt>null</tt>
190	>	*/
191	>	public PriorityQueue(Collection<? extends E> c) {
192	>	initializeArray(c);
193	>	if (c instanceof SortedSet) {
194	>	// @fixme double-cast workaround for compiler
195	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
196	>	comparator = (Comparator<? super E>)s.comparator();
197	>	fillFromSorted(s);
198	>	} else if (c instanceof PriorityQueue) {
199	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
200	>	comparator = (Comparator<? super E>)s.comparator();
201	>	fillFromSorted(s);
202	>	} else {
203	>	comparator = null;
204	>	fillFromUnsorted(c);
205	>	}
206	>	}
207	>
208	>	/**
209	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
210	>	* specified collection.  The priority queue has an initial
211	>	* capacity of 110% of the size of the specified collection or 1
212	>	* if the collection is empty.  This priority queue will be sorted
213	>	* according to the same comparator as the given collection, or
214	>	* according to its elements' natural order if the collection is
215	>	* sorted according to its elements' natural order.
216	>	*
217	>	* @param c the collection whose elements are to be placed
218	>	*        into this priority queue.
219	>	* @throws ClassCastException if elements of the specified collection
220	>	*         cannot be compared to one another according to the priority
221	>	*         queue's ordering.
222	>	* @throws NullPointerException if <tt>c</tt> or any element within it
223	>	* is <tt>null</tt>
224	>	*/
225	>	public PriorityQueue(PriorityQueue<? extends E> c) {
226	>	initializeArray(c);
227	>	comparator = (Comparator<? super E>)c.comparator();
228	>	fillFromSorted(c);
229	>	}
230	>
231	>	/**
232	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
233	>	* specified collection.  The priority queue has an initial
234	>	* capacity of 110% of the size of the specified collection or 1
235	>	* if the collection is empty.  This priority queue will be sorted
236	>	* according to the same comparator as the given collection, or
237	>	* according to its elements' natural order if the collection is
238	>	* sorted according to its elements' natural order.
239	>	*
240	>	* @param c the collection whose elements are to be placed
241	>	*        into this priority queue.
242	>	* @throws ClassCastException if elements of the specified collection
243	>	*         cannot be compared to one another according to the priority
244	>	*         queue's ordering.
245	>	* @throws NullPointerException if <tt>c</tt> or any element within it
246	>	* is <tt>null</tt>
247	>	*/
248	>	public PriorityQueue(SortedSet<? extends E> c) {
249	>	initializeArray(c);
250	>	comparator = (Comparator<? super E>)c.comparator();
251	>	fillFromSorted(c);
252	>	}
253	>
254	>	/**
255	>	* Resize array, if necessary, to be able to hold given index
256	>	*/
257	>	private void grow(int index) {
258	>	int newlen = queue.length;
259	>	if (index < newlen) // don't need to grow
260	>	return;
261	>	if (index == Integer.MAX_VALUE)
262	>	throw new OutOfMemoryError();
263	>	while (newlen <= index) {
264	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
265	>	newlen = Integer.MAX_VALUE;
266	>	else
267	>	newlen <<= 2;
268	>	}
269	>	Object[] newQueue = new Object[newlen];
270	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
271	>	queue = newQueue;
272		}
273	+
274	+	// Queue Methods
275
276	<	public E element() {
277	<	return null;
276	>
277	>
278	>	/**
279	>	* Add the specified element to this priority queue.
280	>	*
281	>	* @return <tt>true</tt>
282	>	* @throws ClassCastException if the specified element cannot be compared
283	>	* with elements currently in the priority queue according
284	>	* to the priority queue's ordering.
285	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
286	>	*/
287	>	public boolean offer(E o) {
288	>	if (o == null)
289	>	throw new NullPointerException();
290	>	modCount++;
291	>	++size;
292	>
293	>	// Grow backing store if necessary
294	>	if (size >= queue.length)
295	>	grow(size);
296	>
297	>	queue[size] = o;
298	>	fixUp(size);
299	>	return true;
300		}
301	+
302		public E poll() {
303	<	return null;
303	>	if (size == 0)
304	>	return null;
305	>	return (E) remove(1);
306		}
307	+
308		public E peek() {
309	<	return null;
309	>	return (E) queue[1];
310		}
311
312	<	public boolean isEmpty() {
312	>	// Collection Methods - the first two override to update docs
313	>
314	>	/**
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	>	* @throws ClassCastException if the specified element cannot be compared
321	>	* with elements currently in the priority queue according
322	>	* to the priority queue's ordering.
323	>	*/
324	>	public boolean add(E o) {
325	>	return super.add(o);
326	>	}
327	>
328	>
329	>	/**
330	>	* Adds all of the elements in the specified collection to this queue.
331	>	* The behavior of this operation is undefined if
332	>	* 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	>	* @throws ClassCastException if any element cannot be compared
340	>	* with elements currently in the priority queue according
341	>	* to the priority queue's ordering.
342	>	*/
343	>	public boolean addAll(Collection<? extends E> c) {
344	>	return super.addAll(c);
345	>	}
346	>
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	>	public boolean remove(Object o) {
363	>	if (o == null)
364	>	return false;
365	>
366	>	if (comparator == null) {
367	>	for (int i = 1; i <= size; i++) {
368	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
369	>	remove(i);
370	>	return true;
371	>	}
372	>	}
373	>	} else {
374	>	for (int i = 1; i <= size; i++) {
375	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
376	>	remove(i);
377	>	return true;
378	>	}
379	>	}
380	>	}
381		return false;
382		}
383	+
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	+	public Iterator<E> iterator() {
391	+	return new Itr();
392	+	}
393	+
394	+	private class Itr implements Iterator<E> {
395	+
396	+	/**
397	+	* Index (into queue array) of element to be returned by
398	+	* subsequent call to next.
399	+	*/
400	+	private int cursor = 1;
401	+
402	+	/**
403	+	* Index of element returned by most recent call to next or
404	+	* previous.  Reset to 0 if this element is deleted by a call
405	+	* to remove.
406	+	*/
407	+	private int lastRet = 0;
408	+
409	+	/**
410	+	* The modCount value that the iterator believes that the backing
411	+	* List should have.  If this expectation is violated, the iterator
412	+	* has detected concurrent modification.
413	+	*/
414	+	private int expectedModCount = modCount;
415	+
416	+	// Workarounds until version that better handles remove() installed.
417	+	// These are used to copy-on-write the array upon first remove
418	+	private Object[] q = queue;
419	+	private int qsize = size;
420	+
421	+	public boolean hasNext() {
422	+	return cursor <= qsize;
423	+	}
424	+
425	+	public E next() {
426	+	checkForComodification();
427	+	if (cursor > qsize)
428	+	throw new NoSuchElementException();
429	+	E result = (E) q[cursor];
430	+	lastRet = cursor++;
431	+	return result;
432	+	}
433	+
434	+	public void remove() {
435	+	if (lastRet == 0)
436	+	throw new IllegalStateException();
437	+	checkForComodification();
438	+
439	+	// Copy on first remove
440	+	if (q == queue) {
441	+	q = new Object[queue.length];
442	+	System.arraycopy(queue, 0, q, 0, queue.length);
443	+	}
444	+	PriorityQueue.this.remove(q[lastRet]);
445	+
446	+	lastRet = 0;
447	+	expectedModCount = modCount;
448	+	}
449	+
450	+	final void checkForComodification() {
451	+	if (modCount != expectedModCount)
452	+	throw new ConcurrentModificationException();
453	+	}
454	+	}
455	+
456		public int size() {
457	<	return 0;
457	>	return size;
458	>	}
459	>
460	>	/**
461	>	* Remove all elements from the priority queue.
462	>	*/
463	>	public void clear() {
464	>	modCount++;
465	>
466	>	// Null out element references to prevent memory leak
467	>	for (int i=1; i<=size; i++)
468	>	queue[i] = null;
469	>
470	>	size = 0;
471		}
472	<	public Object[] toArray() {
473	<	return null;
472	>
473	>	/**
474	>	* Removes and returns the ith element from queue.  Recall
475	>	* that queue is one-based, so 1 <= i <= size.
476	>	*
477	>	*/
478	>	private E remove(int i) {
479	>	assert i <= size;
480	>	modCount++;
481	>
482	>	E result = (E) queue[i];
483	>	queue[i] = queue[size];
484	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
485	>	if (i <= size) {
486	>	fixDown(i);
487	>	fixUp(i);
488	>	}
489	>
490	>	return result;
491	>	}
492	>
493	>	/**
494	>	* Establishes the heap invariant (described above) assuming the heap
495	>	* satisfies the invariant except possibly for the leaf-node indexed by k
496	>	* (which may have a nextExecutionTime less than its parent's).
497	>	*
498	>	* This method functions by "promoting" queue[k] up the hierarchy
499	>	* (by swapping it with its parent) repeatedly until queue[k]
500	>	* is greater than or equal to its parent.
501	>	*/
502	>	private void fixUp(int k) {
503	>	if (comparator == null) {
504	>	while (k > 1) {
505	>	int j = k >> 1;
506	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
507	>	break;
508	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
509	>	k = j;
510	>	}
511	>	} else {
512	>	while (k > 1) {
513	>	int j = k >>> 1;
514	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
515	>	break;
516	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
517	>	k = j;
518	>	}
519	>	}
520		}
521
522	<	public <T> T[] toArray(T[] array) {
523	<	return null;
522	>	/**
523	>	* Establishes the heap invariant (described above) in the subtree
524	>	* rooted at k, which is assumed to satisfy the heap invariant except
525	>	* possibly for node k itself (which may be greater than its children).
526	>	*
527	>	* This method functions by "demoting" queue[k] down the hierarchy
528	>	* (by swapping it with its smaller child) repeatedly until queue[k]
529	>	* is less than or equal to its children.
530	>	*/
531	>	private void fixDown(int k) {
532	>	int j;
533	>	if (comparator == null) {
534	>	while ((j = k << 1) <= size && (j > 0)) {
535	>	if (j<size &&
536	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
537	>	j++; // j indexes smallest kid
538	>
539	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
540	>	break;
541	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
542	>	k = j;
543	>	}
544	>	} else {
545	>	while ((j = k << 1) <= size && (j > 0)) {
546	>	if (j<size &&
547	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
548	>	j++; // j indexes smallest kid
549	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
550	>	break;
551	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
552	>	k = j;
553	>	}
554	>	}
555	>
556	>	}
557	>
558	>
559	>	/**
560	>	* Returns the comparator used to order this collection, or <tt>null</tt>
561	>	* if this collection is sorted according to its elements natural ordering
562	>	* (using <tt>Comparable</tt>).
563	>	*
564	>	* @return the comparator used to order this collection, or <tt>null</tt>
565	>	* if this collection is sorted according to its elements natural ordering.
566	>	*/
567	>	public Comparator<? super E> comparator() {
568	>	return comparator;
569	>	}
570	>
571	>	/**
572	>	* Save the state of the instance to a stream (that
573	>	* is, serialize it).
574	>	*
575	>	* @serialData The length of the array backing the instance is
576	>	* emitted (int), followed by all of its elements (each an
577	>	* <tt>Object</tt>) in the proper order.
578	>	* @param s the stream
579	>	*/
580	>	private void writeObject(java.io.ObjectOutputStream s)
581	>	throws java.io.IOException{
582	>	// Write out element count, and any hidden stuff
583	>	s.defaultWriteObject();
584	>
585	>	// Write out array length
586	>	s.writeInt(queue.length);
587	>
588	>	// Write out all elements in the proper order.
589	>	for (int i=0; i<size; i++)
590	>	s.writeObject(queue[i]);
591	>	}
592	>
593	>	/**
594	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
595	>	* deserialize it).
596	>	* @param s the stream
597	>	*/
598	>	private void readObject(java.io.ObjectInputStream s)
599	>	throws java.io.IOException, ClassNotFoundException {
600	>	// Read in size, and any hidden stuff
601	>	s.defaultReadObject();
602	>
603	>	// Read in array length and allocate array
604	>	int arrayLength = s.readInt();
605	>	queue = new Object[arrayLength];
606	>
607	>	// Read in all elements in the proper order.
608	>	for (int i=0; i<size; i++)
609	>	queue[i] = s.readObject();
610		}
611
612		}
613	+

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