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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package com.github.davidmoten.rtree.internal.util;
import java.util.AbstractQueue;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.SortedSet;
/**
* 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 {@code null} elements. A priority queue
* relying on natural ordering also does not permit insertion of non-comparable
* objects (doing so may result in {@code ClassCastException}).
*
* <p>
* The <em>head</em> of this queue is the <em>least</em> 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 {@code poll}, {@code remove}, {@code peek}, and
* {@code element} access the element at the head of the queue.
*
* <p>
* A priority queue is unbounded, but has an internal <i>capacity</i> 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.
*
* <p>
* This class and its iterator implement all of the <em>optional</em> methods of
* the {@link Collection} and {@link Iterator} interfaces. The Iterator provided
* in method {@link #iterator()} is <em>not</em> guaranteed to traverse the
* elements of the priority queue in any particular order. If you need ordered
* traversal, consider using {@code Arrays.sort(pq.toArray())}.
*
* <p>
* <strong>Note that this implementation is not synchronized.</strong> Multiple
* threads should not access a {@code PriorityQueue} instance concurrently if
* any of the threads modifies the queue. Instead, use the thread-safe
* {@link java.util.concurrent.PriorityBlockingQueue} class.
*
* <p>
* Implementation note: this implementation provides O(log(n)) time for the
* enqueuing and dequeuing methods ({@code offer}, {@code poll},
* {@code remove()} and {@code add}); linear time for the {@code remove(Object)}
* and {@code contains(Object)} methods; and constant time for the retrieval
* methods ({@code peek}, {@code element}, and {@code size}).
*
* <p>
* This class is a member of the <a href=
* "{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
* Framework</a>.
*
* @since 1.5
* @author Josh Bloch, Doug Lea
* @param <E>
* the type of elements held in this collection
*/
public class PriorityQueue<E> extends AbstractQueue<E> 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+1] 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[0], assuming the
* queue is nonempty.
*/
transient Object[] queue; // non-private to simplify nested class access
/**
* 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<? super E> comparator;
/**
* The number of times this priority queue has been <i>structurally
* modified</i>. See AbstractList for gory details.
*/
transient int modCount = 0; // non-private to simplify nested class access
/**
* Creates a {@code 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 {@code 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 {@code initialCapacity} is less than 1
*/
public PriorityQueue(int initialCapacity) {
this(initialCapacity, null);
}
/**
* Creates a {@code PriorityQueue} with the default initial capacity and
* whose elements are ordered according to the specified comparator.
*
* @param comparator
* the comparator that will be used to order this priority queue.
* If {@code null}, the {@linkplain Comparable natural ordering}
* of the elements will be used.
* @since 1.8
*/
public PriorityQueue(Comparator<? super E> comparator) {
this(DEFAULT_INITIAL_CAPACITY, comparator);
}
/**
* Creates a {@code 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 {@code null}, the {@linkplain Comparable natural ordering}
* of the elements will be used.
* @throws IllegalArgumentException
* if {@code initialCapacity} is less than 1
*/
public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
// Note: This restriction of at least one is not actually needed,
// but continues for 1.5 compatibility
if (initialCapacity < 1)
throw new IllegalArgumentException();
this.queue = new Object[initialCapacity];
this.comparator = comparator;
}
/**
* Creates a {@code PriorityQueue} containing the elements in the specified
* collection. If the specified collection is an instance of a
* {@link SortedSet} or is another {@code PriorityQueue}, this priority
* queue will be ordered according to the same ordering. Otherwise, this
* priority queue will be ordered according to the {@linkplain Comparable
* 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
*/
@SuppressWarnings("unchecked")
public PriorityQueue(Collection<? extends E> c) {
if (c instanceof SortedSet<?>) {
SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
this.comparator = (Comparator<? super E>) ss.comparator();
initElementsFromCollection(ss);
} else if (c instanceof PriorityQueue<?>) {
PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
this.comparator = (Comparator<? super E>) pq.comparator();
initFromPriorityQueue(pq);
} else {
this.comparator = null;
initFromCollection(c);
}
}
/**
* Creates a {@code PriorityQueue} containing the elements in the specified
* priority queue. 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 {@code c} cannot be compared to one another
* according to {@code c}'s ordering
* @throws NullPointerException
* if the specified priority queue or any of its elements are
* null
*/
@SuppressWarnings("unchecked")
public PriorityQueue(PriorityQueue<? extends E> c) {
this.comparator = (Comparator<? super E>) c.comparator();
initFromPriorityQueue(c);
}
/**
* Creates a {@code PriorityQueue} containing the elements in the specified
* sorted set. 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
*/
@SuppressWarnings("unchecked")
public PriorityQueue(SortedSet<? extends E> c) {
this.comparator = (Comparator<? super E>) c.comparator();
initElementsFromCollection(c);
}
private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
if (c.getClass() == PriorityQueue.class) {
this.queue = c.toArray();
this.size = c.size();
} else {
initFromCollection(c);
}
}
private void initElementsFromCollection(Collection<? extends E> c) {
Object[] a = c.toArray();
// If c.toArray incorrectly doesn't return Object[], copy it.
if (a.getClass() != Object[].class)
a = Arrays.copyOf(a, a.length, Object[].class);
int len = a.length;
if (len == 1 || this.comparator != null)
for (int i = 0; i < len; i++)
if (a[i] == null)
throw new NullPointerException();
this.queue = a;
this.size = a.length;
}
/**
* Initializes queue array with elements from the given Collection.
*
* @param c
* the collection
*/
private void initFromCollection(Collection<? extends E> c) {
initElementsFromCollection(c);
heapify();
}
/**
* The maximum size of array to allocate. Some VMs reserve some header words
* in an array. Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* Increases the capacity of the array.
*
* @param minCapacity
* the desired minimum capacity
*/
private void grow(int minCapacity) {
int oldCapacity = queue.length;
// Double size if small; else grow by 50%
int newCapacity = oldCapacity
+ ((oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1));
// overflow-conscious code
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
queue = Arrays.copyOf(queue, newCapacity);
}
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;
}
/**
* Inserts the specified element into this priority queue.
*
* @return {@code 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
*/
@Override
public boolean add(E e) {
return offer(e);
}
/**
* Inserts the specified element into this priority queue.
*
* @return {@code 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
*/
@Override
public boolean offer(E e) {
if (e == null)
throw new NullPointerException();
modCount++;
int i = size;
if (i >= queue.length)
grow(i + 1);
size = i + 1;
if (i == 0)
queue[0] = e;
else
siftUp(i, e);
return true;
}
@Override
@SuppressWarnings("unchecked")
public E peek() {
return (size == 0) ? null : (E) queue[0];
}
private int indexOf(Object o) {
if (o != null) {
for (int i = 0; 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 {@code e} such that
* {@code o.equals(e)}, if this queue contains one or more such elements.
* Returns {@code true} if and only 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 {@code true} if this queue changed as a result of the call
*/
@Override
public boolean remove(Object o) {
int i = indexOf(o);
if (i == -1)
return false;
else {
removeAt(i);
return true;
}
}
/**
* Version of remove using reference equality, not equals. Needed by
* iterator.remove.
*
* @param o
* element to be removed from this queue, if present
* @return {@code true} if removed
*/
boolean removeEq(Object o) {
for (int i = 0; i < size; i++) {
if (o == queue[i]) {
removeAt(i);
return true;
}
}
return false;
}
/**
* Returns {@code true} if this queue contains the specified element. More
* formally, returns {@code true} if and only if this queue contains at
* least one element {@code e} such that {@code o.equals(e)}.
*
* @param o
* object to be checked for containment in this queue
* @return {@code true} if this queue contains the specified element
*/
@Override
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.
*
* <p>
* The returned array will be "safe" in that no references to it are
* maintained by this queue. (In other words, this method must allocate a
* new array). The caller is thus free to modify the returned array.
*
* <p>
* This method acts as bridge between array-based and collection-based APIs.
*
* @return an array containing all of the elements in this queue
*/
@Override
public Object[] toArray() {
return Arrays.copyOf(queue, size);
}
/**
* Returns an array containing all of the elements in this queue; the
* runtime type of the returned array is that of the specified array. The
* returned array elements are in no particular order. 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.
*
* <p>
* 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 {@code null}.
*
* <p>
* Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may, under
* certain circumstances, be used to save allocation costs.
*
* <p>
* Suppose {@code x} is a queue known to contain only strings. The following
* code can be used to dump the queue into a newly allocated array of
* {@code String}:
*
* <pre>
* {
* @code
* String[] y = x.toArray(new String[0]);
* }
* </pre>
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
*
* @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 all of the elements in this 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
*/
@Override
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
final int size = this.size;
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOf(queue, size, a.getClass());
System.arraycopy(queue, 0, 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
*/
@Override
public Iterator<E> iterator() {
return new Itr();
}
private final class Itr implements Iterator<E> {
/**
* Index (into queue array) of element to be returned by subsequent call
* to next.
*/
private int cursor = 0;
/**
* Index of element returned by most recent call to next, unless that
* element came from the forgetMeNot list. Set to -1 if element is
* deleted by a call to remove.
*/
private int lastRet = -1;
/**
* A queue 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 siftup instead of a siftdown.) 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 need to store elements in this field.
*/
private ArrayDeque<E> forgetMeNot = null;
/**
* Element returned by the most recent call to next iff that element was
* drawn from the forgetMeNot list.
*/
private E lastRetElt = null;
/**
* The modCount value that the iterator believes that the backing Queue
* should have. If this expectation is violated, the iterator has
* detected concurrent modification.
*/
private int expectedModCount = modCount;
@Override
public boolean hasNext() {
return cursor < size || (forgetMeNot != null && !forgetMeNot.isEmpty());
}
@Override
@SuppressWarnings("unchecked")
public E next() {
if (expectedModCount != modCount)
throw new ConcurrentModificationException();
if (cursor < size)
return (E) queue[lastRet = cursor++];
if (forgetMeNot != null) {
lastRet = -1;
lastRetElt = forgetMeNot.poll();
if (lastRetElt != null)
return lastRetElt;
}
throw new NoSuchElementException();
}
@Override
public void remove() {
if (expectedModCount != modCount)
throw new ConcurrentModificationException();
if (lastRet != -1) {
E moved = PriorityQueue.this.removeAt(lastRet);
lastRet = -1;
if (moved == null)
cursor--;
else {
if (forgetMeNot == null)
forgetMeNot = new ArrayDeque<E>();
forgetMeNot.add(moved);
}
} else if (lastRetElt != null) {
PriorityQueue.this.removeEq(lastRetElt);
lastRetElt = null;
} else {
throw new IllegalStateException();
}
expectedModCount = modCount;
}
}
@Override
public int size() {
return size;
}
/**
* Removes all of the elements from this priority queue. The queue will be
* empty after this call returns.
*/
@Override
public void clear() {
modCount++;
for (int i = 0; i < size; i++)
queue[i] = null;
size = 0;
}
@Override
@SuppressWarnings("unchecked")
public E poll() {
if (size == 0)
return null;
int s = --size;
modCount++;
E result = (E) queue[0];
E x = (E) queue[s];
queue[s] = null;
if (s != 0)
siftDown(0, x);
return result;
}
/**
* Removes the ith element from queue.
*
* Normally this method leaves the elements at up to i-1, inclusive,
* untouched. Under these circumstances, it returns null. Occasionally, in
* order to maintain the heap invariant, it must swap a later element of the
* list with one earlier than i. Under these circumstances, this method
* returns the element that was previously at the end of the list and is now
* at some position before i. This fact is used by iterator.remove so as to
* avoid missing traversing elements.
*/
@SuppressWarnings("unchecked")
private E removeAt(int i) {
// assert i >= 0 && i < size;
modCount++;
int s = --size;
if (s == i) // removed last element
queue[i] = null;
else {
E moved = (E) queue[s];
queue[s] = null;
siftDown(i, moved);
if (queue[i] == moved) {
siftUp(i, moved);
if (queue[i] != moved)
return moved;
}
}
return null;
}
/**
* Inserts item x at position k, maintaining heap invariant by promoting x
* up the tree until it is greater than or equal to its parent, or is the
* root.
*
* To simplify and speed up coercions and comparisons. the Comparable and
* Comparator versions are separated into different methods that are
* otherwise identical. (Similarly for siftDown.)
*
* @param k
* the position to fill
* @param x
* the item to insert
*/
private void siftUp(int k, E x) {
if (comparator != null)
siftUpUsingComparator(k, x);
else
siftUpComparable(k, x);
}
@SuppressWarnings("unchecked")
private void siftUpComparable(int k, E x) {
Comparable<? super E> key = (Comparable<? super E>) x;
while (k > 0) {
int parent = (k - 1) >>> 1;
Object e = queue[parent];
if (key.compareTo((E) e) >= 0)
break;
queue[k] = e;
k = parent;
}
queue[k] = key;
}
@SuppressWarnings("unchecked")
private void siftUpUsingComparator(int k, E x) {
while (k > 0) {
int parent = (k - 1) >>> 1;
Object e = queue[parent];
if (comparator.compare(x, (E) e) >= 0)
break;
queue[k] = e;
k = parent;
}
queue[k] = x;
}
/**
* Inserts item x at position k, maintaining heap invariant by demoting x
* down the tree repeatedly until it is less than or equal to its children
* or is a leaf.
*
* @param k
* the position to fill
* @param x
* the item to insert
*/
private void siftDown(int k, E x) {
if (comparator != null)
siftDownUsingComparator(k, x);
else
siftDownComparable(k, x);
}
@SuppressWarnings("unchecked")
private void siftDownComparable(int k, E x) {
Comparable<? super E> key = (Comparable<? super E>) x;
int half = size >>> 1; // loop while a non-leaf
while (k < half) {
int child = (k << 1) + 1; // assume left child is least
Object c = queue[child];
int right = child + 1;
if (right < size && ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
c = queue[child = right];
if (key.compareTo((E) c) <= 0)
break;
queue[k] = c;
k = child;
}
queue[k] = key;
}
@SuppressWarnings("unchecked")
private void siftDownUsingComparator(int k, E x) {
int half = size >>> 1;
while (k < half) {
int child = (k << 1) + 1;
Object c = queue[child];
int right = child + 1;
if (right < size && comparator.compare((E) c, (E) queue[right]) > 0)
c = queue[child = right];
if (comparator.compare(x, (E) c) <= 0)
break;
queue[k] = c;
k = child;
}
queue[k] = x;
}
/**
* Establishes the heap invariant (described above) in the entire tree,
* assuming nothing about the order of the elements prior to the call.
*/
@SuppressWarnings("unchecked")
private void heapify() {
for (int i = (size >>> 1) - 1; i >= 0; i--)
siftDown(i, (E) queue[i]);
}
/**
* Returns the comparator used to order the elements in this queue, or
* {@code 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 {@code null} if this
* queue is sorted according to the natural ordering of its elements
*/
public Comparator<? super E> comparator() {
return comparator;
}
/**
* Saves this queue to a stream (that is, serializes it).
*
* @serialData The length of the array backing the instance is emitted
* (int), followed by all of its elements (each an
* {@code Object}) in the proper order.
* @param s
* the stream
* @throws java.io.IOException
* when a problem occurs writing the object
*/
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, for compatibility with 1.5 version
s.writeInt(Math.max(2, size + 1));
// Write out all elements in the "proper order".
for (int i = 0; i < size; i++)
s.writeObject(queue[i]);
}
/**
* Reconstitutes the {@code PriorityQueue} instance from a stream (that is,
* deserializes it).
*
* @param s
* the stream
* @throws java.io.IOException
* when a problem occurs reading the object
* @throws ClassNotFoundException
* when an attempt to read the object was made but the class
* corresponding to the serialized object was not on the
* classpath
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in (and discard) array length
s.readInt();
queue = new Object[size];
// Read in all elements.
for (int i = 0; i < size; i++)
queue[i] = s.readObject();
// Elements are guaranteed to be in "proper order", but the
// spec has never explained what that might be.
heapify();
}
}