2 |
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|
3 |
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/** |
4 |
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* An unbounded priority queue based on a priority heap. This queue orders |
5 |
< |
* elements according to the order specified at creation time. This order is |
6 |
< |
* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered |
5 |
> |
* elements according to an order specified at construction time, which is |
6 |
> |
* specified in the same manner as {@link TreeSet} and {@link TreeMap}: elements are ordered |
7 |
|
* either according to their <i>natural order</i> (see {@link Comparable}), or |
8 |
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* according to a {@link Comparator}, depending on which constructor is used. |
9 |
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* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the |
10 |
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* minimal element with respect to the specified ordering. If multiple |
11 |
< |
* these elements are tied for least value, no guarantees are made as to |
12 |
< |
* which of elements is returned. |
11 |
> |
* elements are tied for least value, no guarantees are made as to |
12 |
> |
* which of these elements is returned. |
13 |
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* |
14 |
< |
* <p>Each priority queue has a <i>capacity</i>. The capacity is the size of |
15 |
< |
* the array used to store the elements on the queue. It is always at least |
16 |
< |
* as large as the queue size. As elements are added to a priority list, |
17 |
< |
* its capacity grows automatically. The details of the growth policy are not |
18 |
< |
* specified. |
14 |
> |
* <p>A priority queue has a <i>capacity</i>. The capacity is the |
15 |
> |
* size of the array used internally to store the elements on the |
16 |
> |
* queue. It is always at least as large as the queue size. As |
17 |
> |
* elements are added to a priority queue, its capacity grows |
18 |
> |
* automatically. The details of the growth policy are not specified. |
19 |
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* |
20 |
< |
*<p>Implementation note: this implementation provides O(log(n)) time for |
21 |
< |
* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt> |
22 |
< |
* methods; linear time for the <tt>remove(Object)</tt> and |
23 |
< |
* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>, |
24 |
< |
* <tt>element</tt>, and <tt>size</tt> methods. |
20 |
> |
*<p>Implementation note: this implementation provides O(log(n)) time |
21 |
> |
*for the insertion methods (<tt>offer</tt>, <tt>poll</tt>, |
22 |
> |
*<tt>remove()</tt> and <tt>add</tt>) methods; linear time for the |
23 |
> |
*<tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and |
24 |
> |
*constant time for the retrieval methods (<tt>peek</tt>, |
25 |
> |
*<tt>element</tt>, and <tt>size</tt>). |
26 |
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* |
27 |
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* <p>This class is a member of the |
28 |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
29 |
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* Java Collections Framework</a>. |
30 |
+ |
* @since 1.5 |
31 |
+ |
* @author Josh Bloch |
32 |
|
*/ |
33 |
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public class PriorityQueue<E> extends AbstractQueue<E> |
34 |
< |
implements Queue<E> |
35 |
< |
{ |
34 |
> |
implements Queue<E>, |
35 |
> |
java.io.Serializable { |
36 |
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private static final int DEFAULT_INITIAL_CAPACITY = 11; |
37 |
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|
38 |
|
/** |
39 |
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* Priority queue represented as a balanced binary heap: the two children |
40 |
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* of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is |
41 |
|
* ordered by comparator, or by the elements' natural ordering, if |
42 |
< |
* comparator is null: For each node n in the heap, and each descendant |
43 |
< |
* of n, d, n <= d. |
42 |
> |
* comparator is null: For each node n in the heap and each descendant d |
43 |
> |
* of n, n <= d. |
44 |
|
* |
45 |
< |
* The element with the lowest value is in queue[1] (assuming the queue is |
46 |
< |
* nonempty). A one-based array is used in preference to the traditional |
47 |
< |
* zero-based array to simplify parent and child calculations. |
45 |
> |
* The element with the lowest value is in queue[1], assuming the queue is |
46 |
> |
* nonempty. (A one-based array is used in preference to the traditional |
47 |
> |
* zero-based array to simplify parent and child calculations.) |
48 |
|
* |
49 |
|
* queue.length must be >= 2, even if size == 0. |
50 |
|
*/ |
68 |
|
private transient int modCount = 0; |
69 |
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|
70 |
|
/** |
71 |
< |
* Create a new priority queue with the default initial capacity (11) |
72 |
< |
* that orders its elements according to their natural ordering. |
71 |
> |
* Create a new priority queue with the default initial capacity |
72 |
> |
* (11) that orders its elements according to their natural |
73 |
> |
* ordering (using <tt>Comparable</tt>.) |
74 |
|
*/ |
75 |
|
public PriorityQueue() { |
76 |
|
this(DEFAULT_INITIAL_CAPACITY); |
78 |
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|
79 |
|
/** |
80 |
|
* Create a new priority queue with the specified initial capacity |
81 |
< |
* that orders its elements according to their natural ordering. |
81 |
> |
* that orders its elements according to their natural ordering |
82 |
> |
* (using <tt>Comparable</tt>.) |
83 |
|
* |
84 |
|
* @param initialCapacity the initial capacity for this priority queue. |
85 |
|
*/ |
97 |
|
public PriorityQueue(int initialCapacity, Comparator<E> comparator) { |
98 |
|
if (initialCapacity < 1) |
99 |
|
initialCapacity = 1; |
100 |
< |
queue = new E[initialCapacity + 1]; |
100 |
> |
queue = (E[]) new Object[initialCapacity + 1]; |
101 |
|
this.comparator = comparator; |
102 |
|
} |
103 |
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|
108 |
|
* implements the {@link Sorted} interface, the priority queue will be |
109 |
|
* sorted according to the same comparator, or according to its elements' |
110 |
|
* natural order if the collection is sorted according to its elements' |
111 |
< |
* natural order. If the specified collection does not implement the |
112 |
< |
* <tt>Sorted</tt> interface, the priority queue is ordered according to |
111 |
> |
* natural order. If the specified collection does not implement |
112 |
> |
* <tt>Sorted</tt>, the priority queue is ordered according to |
113 |
|
* its elements' natural order. |
114 |
|
* |
115 |
|
* @param initialElements the collection whose elements are to be placed |
126 |
|
Integer.MAX_VALUE - 1); |
127 |
|
if (initialCapacity < 1) |
128 |
|
initialCapacity = 1; |
129 |
< |
queue = new E[initialCapacity + 1]; |
129 |
> |
queue = (E[]) new Object[initialCapacity + 1]; |
130 |
|
|
126 |
– |
/* Commented out to compile with generics compiler |
131 |
|
|
132 |
|
if (initialElements instanceof Sorted) { |
133 |
|
comparator = ((Sorted)initialElements).comparator(); |
134 |
|
for (Iterator<E> i = initialElements.iterator(); i.hasNext(); ) |
135 |
|
queue[++size] = i.next(); |
136 |
|
} else { |
133 |
– |
*/ |
134 |
– |
{ |
137 |
|
comparator = null; |
138 |
|
for (Iterator<E> i = initialElements.iterator(); i.hasNext(); ) |
139 |
|
add(i.next()); |
143 |
|
// Queue Methods |
144 |
|
|
145 |
|
/** |
146 |
< |
* Remove and return the minimal element from this priority queue if |
147 |
< |
* it contains one or more elements, otherwise <tt>null</tt>. The term |
148 |
< |
* <i>minimal</i> is defined according to this priority queue's order. |
146 |
> |
* Remove and return the minimal element from this priority queue |
147 |
> |
* if it contains one or more elements, otherwise return |
148 |
> |
* <tt>null</tt>. The term <i>minimal</i> is defined according to |
149 |
> |
* this priority queue's order. |
150 |
|
* |
151 |
|
* @return the minimal element from this priority queue if it contains |
152 |
|
* one or more elements, otherwise <tt>null</tt>. |
158 |
|
} |
159 |
|
|
160 |
|
/** |
161 |
< |
* Return, but do not remove, the minimal element from the priority queue, |
162 |
< |
* or <tt>null</tt> if the queue is empty. The term <i>minimal</i> is |
163 |
< |
* defined according to this priority queue's order. This method returns |
164 |
< |
* the same object reference that would be returned by by the |
165 |
< |
* <tt>poll</tt> method. The two methods differ in that this method |
166 |
< |
* does not remove the element from the priority queue. |
161 |
> |
* Return, but do not remove, the minimal element from the |
162 |
> |
* priority queue, or return <tt>null</tt> if the queue is empty. |
163 |
> |
* The term <i>minimal</i> is defined according to this priority |
164 |
> |
* queue's order. This method returns the same object reference |
165 |
> |
* that would be returned by by the <tt>poll</tt> method. The two |
166 |
> |
* methods differ in that this method does not remove the element |
167 |
> |
* from the priority queue. |
168 |
|
* |
169 |
|
* @return the minimal element from this priority queue if it contains |
170 |
|
* one or more elements, otherwise <tt>null</tt>. |
181 |
|
* specified element (or equivalently, if this collection changed as a |
182 |
|
* result of the call). |
183 |
|
* |
184 |
< |
* @param o element to be removed from this collection, if present. |
184 |
> |
* @param element the element to be removed from this collection, |
185 |
> |
* if present. |
186 |
|
* @return <tt>true</tt> if this collection changed as a result of the |
187 |
|
* call |
188 |
|
* @throws ClassCastException if the specified element cannot be compared |
189 |
< |
* with elements currently in the priority queue according |
189 |
> |
* with elements currently in the priority queue according |
190 |
|
* to the priority queue's ordering. |
191 |
|
* @throws NullPointerException if the specified element is null. |
192 |
|
*/ |
214 |
|
|
215 |
|
/** |
216 |
|
* Returns an iterator over the elements in this priority queue. The |
217 |
< |
* first element returned by this iterator is the same element that |
218 |
< |
* would be returned by a call to <tt>peek</tt>. |
219 |
< |
* |
217 |
> |
* elements of the priority queue will be returned by this iterator in the |
218 |
> |
* order specified by the queue, which is to say the order they would be |
219 |
> |
* returned by repeated calls to <tt>poll</tt>. |
220 |
> |
* |
221 |
|
* @return an <tt>Iterator</tt> over the elements in this priority queue. |
222 |
|
*/ |
223 |
|
public Iterator<E> iterator() { |
224 |
< |
return new Itr(); |
224 |
> |
return new Itr(); |
225 |
|
} |
226 |
|
|
227 |
|
private class Itr implements Iterator<E> { |
228 |
< |
/** |
229 |
< |
* Index (into queue array) of element to be returned by |
228 |
> |
/** |
229 |
> |
* Index (into queue array) of element to be returned by |
230 |
|
* subsequent call to next. |
231 |
< |
*/ |
232 |
< |
int cursor = 1; |
231 |
> |
*/ |
232 |
> |
private int cursor = 1; |
233 |
> |
|
234 |
> |
/** |
235 |
> |
* Index of element returned by most recent call to next or |
236 |
> |
* previous. Reset to 0 if this element is deleted by a call |
237 |
> |
* to remove. |
238 |
> |
*/ |
239 |
> |
private int lastRet = 0; |
240 |
> |
|
241 |
> |
/** |
242 |
> |
* The modCount value that the iterator believes that the backing |
243 |
> |
* List should have. If this expectation is violated, the iterator |
244 |
> |
* has detected concurrent modification. |
245 |
> |
*/ |
246 |
> |
private int expectedModCount = modCount; |
247 |
|
|
248 |
< |
/** |
249 |
< |
* Index of element returned by most recent call to next or |
250 |
< |
* previous. Reset to 0 if this element is deleted by a call |
231 |
< |
* to remove. |
232 |
< |
*/ |
233 |
< |
int lastRet = 0; |
234 |
< |
|
235 |
< |
/** |
236 |
< |
* The modCount value that the iterator believes that the backing |
237 |
< |
* List should have. If this expectation is violated, the iterator |
238 |
< |
* has detected concurrent modification. |
239 |
< |
*/ |
240 |
< |
int expectedModCount = modCount; |
241 |
< |
|
242 |
< |
public boolean hasNext() { |
243 |
< |
return cursor <= size; |
244 |
< |
} |
248 |
> |
public boolean hasNext() { |
249 |
> |
return cursor <= size; |
250 |
> |
} |
251 |
|
|
252 |
< |
public E next() { |
252 |
> |
public E next() { |
253 |
|
checkForComodification(); |
254 |
|
if (cursor > size) |
255 |
< |
throw new NoSuchElementException(); |
255 |
> |
throw new NoSuchElementException(); |
256 |
|
E result = queue[cursor]; |
257 |
|
lastRet = cursor++; |
258 |
|
return result; |
259 |
< |
} |
259 |
> |
} |
260 |
|
|
261 |
< |
public void remove() { |
262 |
< |
if (lastRet == 0) |
263 |
< |
throw new IllegalStateException(); |
261 |
> |
public void remove() { |
262 |
> |
if (lastRet == 0) |
263 |
> |
throw new IllegalStateException(); |
264 |
|
checkForComodification(); |
265 |
|
|
266 |
|
PriorityQueue.this.remove(lastRet); |
268 |
|
cursor--; |
269 |
|
lastRet = 0; |
270 |
|
expectedModCount = modCount; |
271 |
< |
} |
271 |
> |
} |
272 |
|
|
273 |
< |
final void checkForComodification() { |
274 |
< |
if (modCount != expectedModCount) |
275 |
< |
throw new ConcurrentModificationException(); |
276 |
< |
} |
273 |
> |
final void checkForComodification() { |
274 |
> |
if (modCount != expectedModCount) |
275 |
> |
throw new ConcurrentModificationException(); |
276 |
> |
} |
277 |
|
} |
278 |
|
|
279 |
|
/** |
280 |
|
* Returns the number of elements in this priority queue. |
281 |
< |
* |
281 |
> |
* |
282 |
|
* @return the number of elements in this priority queue. |
283 |
|
*/ |
284 |
|
public int size() { |
291 |
|
* @param element the element to add. |
292 |
|
* @return true |
293 |
|
* @throws ClassCastException if the specified element cannot be compared |
294 |
< |
* with elements currently in the priority queue according |
294 |
> |
* with elements currently in the priority queue according |
295 |
|
* to the priority queue's ordering. |
296 |
|
* @throws NullPointerException if the specified element is null. |
297 |
|
*/ |
299 |
|
if (element == null) |
300 |
|
throw new NullPointerException(); |
301 |
|
modCount++; |
302 |
+ |
++size; |
303 |
|
|
304 |
|
// Grow backing store if necessary |
305 |
< |
if (++size == queue.length) { |
306 |
< |
E[] newQueue = new E[2 * queue.length]; |
307 |
< |
System.arraycopy(queue, 0, newQueue, 0, size); |
305 |
> |
while (size >= queue.length) { |
306 |
> |
E[] newQueue = (E[]) new Object[2 * queue.length]; |
307 |
> |
System.arraycopy(queue, 0, newQueue, 0, queue.length); |
308 |
|
queue = newQueue; |
309 |
|
} |
310 |
|
|
411 |
|
* <tt>null</tt> if it uses its elements' natural ordering. |
412 |
|
* |
413 |
|
* @return the comparator associated with this priority queue, or |
414 |
< |
* <tt>null</tt> if it uses its elements' natural ordering. |
414 |
> |
* <tt>null</tt> if it uses its elements' natural ordering. |
415 |
|
*/ |
416 |
< |
Comparator comparator() { |
416 |
> |
public Comparator comparator() { |
417 |
|
return comparator; |
418 |
|
} |
419 |
|
|
424 |
|
* @serialData The length of the array backing the instance is |
425 |
|
* emitted (int), followed by all of its elements (each an |
426 |
|
* <tt>Object</tt>) in the proper order. |
427 |
+ |
* @param s the stream |
428 |
|
*/ |
429 |
|
private synchronized void writeObject(java.io.ObjectOutputStream s) |
430 |
|
throws java.io.IOException{ |
431 |
< |
// Write out element count, and any hidden stuff |
432 |
< |
s.defaultWriteObject(); |
431 |
> |
// Write out element count, and any hidden stuff |
432 |
> |
s.defaultWriteObject(); |
433 |
|
|
434 |
|
// Write out array length |
435 |
|
s.writeInt(queue.length); |
436 |
|
|
437 |
< |
// Write out all elements in the proper order. |
438 |
< |
for (int i=0; i<size; i++) |
437 |
> |
// Write out all elements in the proper order. |
438 |
> |
for (int i=0; i<size; i++) |
439 |
|
s.writeObject(queue[i]); |
440 |
|
} |
441 |
|
|
442 |
|
/** |
443 |
|
* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is, |
444 |
|
* deserialize it). |
445 |
+ |
* @param s the stream |
446 |
|
*/ |
447 |
|
private synchronized void readObject(java.io.ObjectInputStream s) |
448 |
|
throws java.io.IOException, ClassNotFoundException { |
449 |
< |
// Read in size, and any hidden stuff |
450 |
< |
s.defaultReadObject(); |
449 |
> |
// Read in size, and any hidden stuff |
450 |
> |
s.defaultReadObject(); |
451 |
|
|
452 |
|
// Read in array length and allocate array |
453 |
|
int arrayLength = s.readInt(); |
454 |
< |
queue = new E[arrayLength]; |
454 |
> |
queue = (E[]) new Object[arrayLength]; |
455 |
|
|
456 |
< |
// Read in all elements in the proper order. |
457 |
< |
for (int i=0; i<size; i++) |
456 |
> |
// Read in all elements in the proper order. |
457 |
> |
for (int i=0; i<size; i++) |
458 |
|
queue[i] = (E)s.readObject(); |
459 |
|
} |
460 |
|
|