/*
* @(#)PriorityQueue.java 1.8 05/08/27
*
* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util;
import java.util.*; // for javadoc (till 6280605 is fixed)
/**
* An unbounded priority {@linkplain Queue queue} based on a priority
* heap. The elements of the priority queue are ordered according to
* their {@linkplain Comparable natural ordering}, or by a {@link
* Comparator} provided at queue construction time, depending on which
* constructor is used. A priority queue does not permit
* null elements. A priority queue relying on natural
* ordering also does not permit insertion of non-comparable objects
* (doing so may result in ClassCastException).
*
* The head of this queue is the least element
* with respect to the specified ordering. If multiple elements are
* tied for least value, the head is one of those elements -- ties are
* broken arbitrarily. The queue retrieval operations poll,
* remove, peek, and element access the
* element at the head of the queue.
*
*
A priority queue is unbounded, but has an internal
* capacity governing the size of an array used to store the
* elements on the queue. It is always at least as large as the queue
* size. As elements are added to a priority queue, its capacity
* grows automatically. The details of the growth policy are not
* specified.
*
*
This class and its iterator implement all of the
* optional methods of the {@link Collection} and {@link
* Iterator} interfaces. The Iterator provided in method {@link
* #iterator()} is not guaranteed to traverse the elements of
* the priority queue in any particular order. If you need ordered
* traversal, consider using Arrays.sort(pq.toArray()).
*
*
Note that this implementation is not synchronized.
* Multiple threads should not access a PriorityQueue
* instance concurrently if any of the threads modifies the list
* structurally. Instead, use the thread-safe {@link
* java.util.concurrent.PriorityBlockingQueue} class.
*
*
Implementation note: this implementation provides O(log(n)) time
* for the insertion methods (offer, poll,
* remove() and add) methods; linear time for the
* remove(Object) and contains(Object) methods; and
* constant time for the retrieval methods (peek,
* element, and size).
*
*
This class is a member of the
*
* Java Collections Framework.
* @since 1.5
* @version 1.8, 08/27/05
* @author Josh Bloch
* @param the type of elements held in this collection
*/
public class PriorityQueue extends AbstractQueue
implements java.io.Serializable {
private static final long serialVersionUID = -7720805057305804111L;
private static final int DEFAULT_INITIAL_CAPACITY = 11;
/**
* Priority queue represented as a balanced binary heap: the two children
* of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is
* ordered by comparator, or by the elements' natural ordering, if
* comparator is null: For each node n in the heap and each descendant d
* of n, n <= d.
*
* The element with the lowest value is in queue[1], assuming the queue is
* nonempty. (A one-based array is used in preference to the traditional
* zero-based array to simplify parent and child calculations.)
*
* queue.length must be >= 2, even if size == 0.
*/
private transient Object[] queue;
/**
* The number of elements in the priority queue.
*/
private int size = 0;
/**
* The comparator, or null if priority queue uses elements'
* natural ordering.
*/
private final Comparator comparator;
/**
* The number of times this priority queue has been
* structurally modified. See AbstractList for gory details.
*/
private transient int modCount = 0;
/**
* Creates a PriorityQueue with the default initial
* capacity (11) that orders its elements according to their
* {@linkplain Comparable natural ordering}.
*/
public PriorityQueue() {
this(DEFAULT_INITIAL_CAPACITY, null);
}
/**
* Creates a PriorityQueue with the specified initial
* capacity that orders its elements according to their
* {@linkplain Comparable natural ordering}.
*
* @param initialCapacity the initial capacity for this priority queue
* @throws IllegalArgumentException if initialCapacity is less
* than 1
*/
public PriorityQueue(int initialCapacity) {
this(initialCapacity, null);
}
/**
* Creates a PriorityQueue with the specified initial capacity
* that orders its elements according to the specified comparator.
*
* @param initialCapacity the initial capacity for this priority queue
* @param comparator the comparator that will be used to order
* this priority queue. If null, the natural
* ordering of the elements will be used.
* @throws IllegalArgumentException if initialCapacity is
* less than 1
*/
public PriorityQueue(int initialCapacity,
Comparator comparator) {
if (initialCapacity < 1)
throw new IllegalArgumentException();
this.queue = new Object[initialCapacity + 1];
this.comparator = comparator;
}
/**
* Common code to initialize underlying queue array across
* constructors below.
*/
private void initializeArray(Collection c) {
int sz = c.size();
int initialCapacity = (int)Math.min((sz * 110L) / 100,
Integer.MAX_VALUE - 1);
if (initialCapacity < 1)
initialCapacity = 1;
this.queue = new Object[initialCapacity + 1];
}
/**
* Initially fill elements of the queue array under the
* knowledge that it is sorted or is another PQ, in which
* case we can just place the elements in the order presented.
*/
private void fillFromSorted(Collection c) {
for (Iterator i = c.iterator(); i.hasNext(); ) {
int k = ++size;
if (k >= queue.length)
grow(k);
queue[k] = i.next();
}
}
/**
* Initially fill elements of the queue array that is not to our knowledge
* sorted, so we must rearrange the elements to guarantee the heap
* invariant.
*/
private void fillFromUnsorted(Collection c) {
for (Iterator i = c.iterator(); i.hasNext(); ) {
int k = ++size;
if (k >= queue.length)
grow(k);
queue[k] = i.next();
}
heapify();
}
/**
* Creates a PriorityQueue containing the elements in the
* specified collection. The priority queue has an initial
* capacity of 110% of the size of the specified collection or 1
* if the collection is empty. If the specified collection is an
* instance of a {@link java.util.SortedSet} or is another
* PriorityQueue, the priority queue will be ordered
* according to the same ordering. Otherwise, this priority queue
* will be ordered according to the natural ordering of its elements.
*
* @param c the collection whose elements are to be placed
* into this priority queue
* @throws ClassCastException if elements of the specified collection
* cannot be compared to one another according to the priority
* queue's ordering
* @throws NullPointerException if the specified collection or any
* of its elements are null
*/
public PriorityQueue(Collection c) {
initializeArray(c);
if (c instanceof SortedSet) {
SortedSet s = (SortedSet)c;
comparator = (Comparator)s.comparator();
fillFromSorted(s);
} else if (c instanceof PriorityQueue) {
PriorityQueue s = (PriorityQueue) c;
comparator = (Comparator)s.comparator();
fillFromSorted(s);
} else {
comparator = null;
fillFromUnsorted(c);
}
}
/**
* Creates a PriorityQueue containing the elements in the
* specified priority queue. The priority queue has an initial
* capacity of 110% of the size of the specified priority queue or
* 1 if the priority queue is empty. This priority queue will be
* ordered according to the same ordering as the given priority
* queue.
*
* @param c the priority queue whose elements are to be placed
* into this priority queue
* @throws ClassCastException if elements of c cannot be
* compared to one another according to c's
* ordering
* @throws NullPointerException if the specified priority queue or any
* of its elements are null
*/
public PriorityQueue(PriorityQueue c) {
initializeArray(c);
comparator = (Comparator)c.comparator();
fillFromSorted(c);
}
/**
* Creates a PriorityQueue containing the elements in the
* specified sorted set. The priority queue has an initial
* capacity of 110% of the size of the specified sorted set or 1
* if the sorted set is empty. This priority queue will be ordered
* according to the same ordering as the given sorted set.
*
* @param c the sorted set whose elements are to be placed
* into this priority queue.
* @throws ClassCastException if elements of the specified sorted
* set cannot be compared to one another according to the
* sorted set's ordering
* @throws NullPointerException if the specified sorted set or any
* of its elements are null
*/
public PriorityQueue(SortedSet c) {
initializeArray(c);
comparator = (Comparator)c.comparator();
fillFromSorted(c);
}
/**
* Resize array, if necessary, to be able to hold given index.
*/
private void grow(int index) {
int newlen = queue.length;
if (index < newlen) // don't need to grow
return;
if (index == Integer.MAX_VALUE)
throw new OutOfMemoryError();
while (newlen <= index) {
if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow
newlen = Integer.MAX_VALUE;
else
newlen <<= 2;
}
queue = Arrays.copyOf(queue, newlen);
}
/**
* Inserts the specified element into this priority queue.
*
* @return true (as specified by {@link Collection#add})
* @throws ClassCastException if the specified element cannot be
* compared with elements currently in this priority queue
* according to the priority queue's ordering
* @throws NullPointerException if the specified element is null
*/
public boolean add(E e) {
return offer(e);
}
/**
* Inserts the specified element into this priority queue.
*
* @return true (as specified by {@link Queue#offer})
* @throws ClassCastException if the specified element cannot be
* compared with elements currently in this priority queue
* according to the priority queue's ordering
* @throws NullPointerException if the specified element is null
*/
public boolean offer(E e) {
if (e == null)
throw new NullPointerException();
modCount++;
++size;
// Grow backing store if necessary
if (size >= queue.length)
grow(size);
queue[size] = e;
fixUp(size);
return true;
}
public E peek() {
if (size == 0)
return null;
return (E) queue[1];
}
private int indexOf(Object o) {
if (o == null)
return -1;
for (int i = 1; i <= size; i++)
if (o.equals(queue[i]))
return i;
return -1;
}
/**
* Removes a single instance of the specified element from this queue,
* if it is present. More formally, removes an element e such
* that o.equals(e), if this queue contains one or more such
* elements. Returns true if this queue contained the specified element
* (or equivalently, if this queue changed as a result of the call).
*
* @param o element to be removed from this queue, if present
* @return true if this queue changed as a result of the call
*/
public boolean remove(Object o) {
int i = indexOf(o);
if (i == -1)
return false;
else {
removeAt(i);
return true;
}
}
/**
* Returns true if this queue contains the specified element.
* More formally, returns true if and only if this queue contains
* at least one element e such that o.equals(e).
*
* @param o object to be checked for containment in this queue
* @return true if this queue contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o) != -1;
}
/**
* Returns an array containing all of the elements in this queue,
* The elements are in no particular order.
*
* The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* @return an array containing all of the elements in this queue.
*/
public Object[] toArray() {
return Arrays.copyOfRange(queue, 1, size+1);
}
/**
* Returns an array containing all of the elements in this queue.
* The elements are in no particular order. The runtime type of
* the returned array is that of the specified array. If the queue
* fits in the specified array, it is returned therein.
* Otherwise, a new array is allocated with the runtime type of
* the specified array and the size of this queue.
*
*
If the queue fits in the specified array with room to spare
* (i.e., the array has more elements than the queue), the element in
* the array immediately following the end of the collection is set to
* null. (This is useful in determining the length of the
* queue only if the caller knows that the queue does not contain
* any null elements.)
*
* @param a the array into which the elements of the queue are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the queue
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this queue
* @throws NullPointerException if the specified array is null
*/
public T[] toArray(T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOfRange(queue, 1, size+1, a.getClass());
System.arraycopy(queue, 1, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
/**
* Returns an iterator over the elements in this queue. The iterator
* does not return the elements in any particular order.
*
* @return an iterator over the elements in this queue
*/
public Iterator iterator() {
return new Itr();
}
private class Itr implements Iterator {
/**
* Index (into queue array) of element to be returned by
* subsequent call to next.
*/
private int cursor = 1;
/**
* Index of element returned by most recent call to next,
* unless that element came from the forgetMeNot list.
* Reset to 0 if element is deleted by a call to remove.
*/
private int lastRet = 0;
/**
* The modCount value that the iterator believes that the backing
* List should have. If this expectation is violated, the iterator
* has detected concurrent modification.
*/
private int expectedModCount = modCount;
/**
* A list of elements that were moved from the unvisited portion of
* the heap into the visited portion as a result of "unlucky" element
* removals during the iteration. (Unlucky element removals are those
* that require a fixup instead of a fixdown.) We must visit all of
* the elements in this list to complete the iteration. We do this
* after we've completed the "normal" iteration.
*
* We expect that most iterations, even those involving removals,
* will not use need to store elements in this field.
*/
private ArrayList forgetMeNot = null;
/**
* Element returned by the most recent call to next iff that
* element was drawn from the forgetMeNot list.
*/
private Object lastRetElt = null;
public boolean hasNext() {
return cursor <= size || forgetMeNot != null;
}
public E next() {
checkForComodification();
E result;
if (cursor <= size) {
result = (E) queue[cursor];
lastRet = cursor++;
}
else if (forgetMeNot == null)
throw new NoSuchElementException();
else {
int remaining = forgetMeNot.size();
result = forgetMeNot.remove(remaining - 1);
if (remaining == 1)
forgetMeNot = null;
lastRet = 0;
lastRetElt = result;
}
return result;
}
public void remove() {
checkForComodification();
if (lastRet != 0) {
E moved = PriorityQueue.this.removeAt(lastRet);
lastRet = 0;
if (moved == null) {
cursor--;
} else {
if (forgetMeNot == null)
forgetMeNot = new ArrayList();
forgetMeNot.add(moved);
}
} else if (lastRetElt != null) {
PriorityQueue.this.remove(lastRetElt);
lastRetElt = null;
} else {
throw new IllegalStateException();
}
expectedModCount = modCount;
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
public int size() {
return size;
}
/**
* Removes all of the elements from this priority queue.
* The queue will be empty after this call returns.
*/
public void clear() {
modCount++;
// Null out element references to prevent memory leak
for (int i=1; i<=size; i++)
queue[i] = null;
size = 0;
}
public E poll() {
if (size == 0)
return null;
modCount++;
E result = (E) queue[1];
queue[1] = queue[size];
queue[size--] = null; // Drop extra ref to prevent memory leak
if (size > 1)
fixDown(1);
return result;
}
/**
* Removes and returns the ith element from queue. (Recall that queue
* is one-based, so 1 <= i <= size.)
*
* Normally this method leaves the elements at positions from 1 up to i-1,
* inclusive, untouched. Under these circumstances, it returns null.
* Occasionally, in order to maintain the heap invariant, it must move
* the last element of the list to some index in the range [2, i-1],
* and move the element previously at position (i/2) to position i.
* Under these circumstances, this method returns the element that was
* previously at the end of the list and is now at some position between
* 2 and i-1 inclusive.
*/
private E removeAt(int i) {
assert i > 0 && i <= size;
modCount++;
E moved = (E) queue[size];
queue[i] = moved;
queue[size--] = null; // Drop extra ref to prevent memory leak
if (i <= size) {
fixDown(i);
if (queue[i] == moved) {
fixUp(i);
if (queue[i] != moved)
return moved;
}
}
return null;
}
/**
* Establishes the heap invariant (described above) assuming the heap
* satisfies the invariant except possibly for the leaf-node indexed by k
* (which may have a nextExecutionTime less than its parent's).
*
* This method functions by "promoting" queue[k] up the hierarchy
* (by swapping it with its parent) repeatedly until queue[k]
* is greater than or equal to its parent.
*/
private void fixUp(int k) {
if (comparator == null) {
while (k > 1) {
int j = k >> 1;
if (((Comparable)queue[j]).compareTo((E)queue[k]) <= 0)
break;
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
} else {
while (k > 1) {
int j = k >>> 1;
if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
break;
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
}
/**
* Establishes the heap invariant (described above) in the subtree
* rooted at k, which is assumed to satisfy the heap invariant except
* possibly for node k itself (which may be greater than its children).
*
* This method functions by "demoting" queue[k] down the hierarchy
* (by swapping it with its smaller child) repeatedly until queue[k]
* is less than or equal to its children.
*/
private void fixDown(int k) {
int j;
if (comparator == null) {
while ((j = k << 1) <= size && (j > 0)) {
if (j)queue[j]).compareTo((E)queue[j+1]) > 0)
j++; // j indexes smallest kid
if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0)
break;
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
} else {
while ((j = k << 1) <= size && (j > 0)) {
if (j 0)
j++; // j indexes smallest kid
if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
break;
Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
}
/**
* Establishes the heap invariant (described above) in the entire tree,
* assuming nothing about the order of the elements prior to the call.
*/
private void heapify() {
for (int i = size/2; i >= 1; i--)
fixDown(i);
}
/**
* Returns the comparator used to order the elements in this
* queue, or null if this queue is sorted according to
* the {@linkplain Comparable natural ordering} of its elements.
*
* @return the comparator used to order this queue, or
* null if this queue is sorted according to the
* natural ordering of its elements.
*/
public Comparator comparator() {
return comparator;
}
/**
* Save the state of the instance to a stream (that
* is, serialize it).
*
* @serialData The length of the array backing the instance is
* emitted (int), followed by all of its elements (each an
* Object) in the proper order.
* @param s the stream
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
s.defaultWriteObject();
// Write out array length
s.writeInt(queue.length);
// Write out all elements in the proper order.
for (int i=1; i<=size; i++)
s.writeObject(queue[i]);
}
/**
* Reconstitute the PriorityQueue instance from a stream
* (that is, deserialize it).
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in array length and allocate array
int arrayLength = s.readInt();
queue = new Object[arrayLength];
// Read in all elements in the proper order.
for (int i=1; i<=size; i++)
queue[i] = (E) s.readObject();
}
}