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	/*
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* Written by Josh Bloch of Google Inc. and released to the public domain,
	* as explained at http://creativecommons.org/publicdomain/zero/1.0/.
	*/

	package java.util;

	import java.io.Serializable;
	import java.util.function.Consumer;
	import sun.misc.SharedSecrets;

	/**
	* Resizable-array implementation of the {@link Deque} interface. Array
	* deques have no capacity restrictions; they grow as necessary to support
	* usage. They are not thread-safe; in the absence of external
	* synchronization, they do not support concurrent access by multiple threads.
	* Null elements are prohibited. This class is likely to be faster than
	* {@link Stack} when used as a stack, and faster than {@link LinkedList}
	* when used as a queue.
	*
	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
	* Exceptions include {@link #remove(Object) remove}, {@link
	* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
	* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
	* iterator.remove()}, and the bulk operations, all of which run in linear
	* time.
	*
	* <p>The iterators returned by this class's {@code iterator} method are
	* <i>fail-fast</i>: If the deque is modified at any time after the iterator
	* is created, in any way except through the iterator's own {@code remove}
	* method, the iterator will generally throw a {@link
	* ConcurrentModificationException}. Thus, in the face of concurrent
	* modification, the iterator fails quickly and cleanly, rather than risking
	* arbitrary, non-deterministic behavior at an undetermined time in the
	* future.
	*
	* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
	* as it is, generally speaking, impossible to make any hard guarantees in the
	* presence of unsynchronized concurrent modification. Fail-fast iterators
	* throw {@code ConcurrentModificationException} on a best-effort basis.
	* Therefore, it would be wrong to write a program that depended on this
	* exception for its correctness: <i>the fail-fast behavior of iterators
	* should be used only to detect bugs.</i>
	*
	* <p>This class and its iterator implement all of the
	* <em>optional</em> methods of the {@link Collection} and {@link
	* Iterator} interfaces.
	*
	* <p>This class is a member of the
	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
	* Java Collections Framework</a>.
	*
	* @author Josh Bloch and Doug Lea
	* @since 1.6
	* @param <E> the type of elements held in this collection
	*/
	public class ArrayDeque<E> extends AbstractCollection<E>
	implements Deque<E>, Cloneable, Serializable
	{
	/**
	* The array in which the elements of the deque are stored.
	* The capacity of the deque is the length of this array, which is
	* always a power of two. The array is never allowed to become
	* full, except transiently within an addX method where it is
	* resized (see doubleCapacity) immediately upon becoming full,
	* thus avoiding head and tail wrapping around to equal each
	* other. We also guarantee that all array cells not holding
	* deque elements are always null.
	*/
	transient Object[] elements; // non-private to simplify nested class access

	/**
	* The index of the element at the head of the deque (which is the
	* element that would be removed by remove() or pop()); or an
	* arbitrary number equal to tail if the deque is empty.
	*/
	transient int head;

	/**
	* The index at which the next element would be added to the tail
	* of the deque (via addLast(E), add(E), or push(E)).
	*/
	transient int tail;

	/**
	* The minimum capacity that we'll use for a newly created deque.
	* Must be a power of 2.
	*/
	private static final int MIN_INITIAL_CAPACITY = 8;

	// **** Array allocation and resizing utilities ****

	private static int calculateSize(int numElements) {
	int initialCapacity = MIN_INITIAL_CAPACITY;
	// Find the best power of two to hold elements.
	// Tests "<=" because arrays aren't kept full.
	if (numElements >= initialCapacity) {
	initialCapacity = numElements;
	initialCapacity \|= (initialCapacity >>> 1);
	initialCapacity \|= (initialCapacity >>> 2);
	initialCapacity \|= (initialCapacity >>> 4);
	initialCapacity \|= (initialCapacity >>> 8);
	initialCapacity \|= (initialCapacity >>> 16);
	initialCapacity++;

	if (initialCapacity < 0) // Too many elements, must back off
	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
	}
	return initialCapacity;
	}

	/**
	* Allocates empty array to hold the given number of elements.
	*
	* @param numElements the number of elements to hold
	*/
	private void allocateElements(int numElements) {
	elements = new Object[calculateSize(numElements)];
	}

	/**
	* Doubles the capacity of this deque. Call only when full, i.e.,
	* when head and tail have wrapped around to become equal.
	*/
	private void doubleCapacity() {
	assert head == tail;
	int p = head;
	int n = elements.length;
	int r = n - p; // number of elements to the right of p
	int newCapacity = n << 1;
	if (newCapacity < 0)
	throw new IllegalStateException("Sorry, deque too big");
	Object[] a = new Object[newCapacity];
	System.arraycopy(elements, p, a, 0, r);
	System.arraycopy(elements, 0, a, r, p);
	elements = a;
	head = 0;
	tail = n;
	}

	/**
	* Copies the elements from our element array into the specified array,
	* in order (from first to last element in the deque). It is assumed
	* that the array is large enough to hold all elements in the deque.
	*
	* @return its argument
	*/
	private <T> T[] copyElements(T[] a) {
	if (head < tail) {
	System.arraycopy(elements, head, a, 0, size());
	} else if (head > tail) {
	int headPortionLen = elements.length - head;
	System.arraycopy(elements, head, a, 0, headPortionLen);
	System.arraycopy(elements, 0, a, headPortionLen, tail);
	}
	return a;
	}

	/**
	* Constructs an empty array deque with an initial capacity
	* sufficient to hold 16 elements.
	*/
	public ArrayDeque() {
	elements = new Object[16];
	}

	/**
	* Constructs an empty array deque with an initial capacity
	* sufficient to hold the specified number of elements.
	*
	* @param numElements lower bound on initial capacity of the deque
	*/
	public ArrayDeque(int numElements) {
	allocateElements(numElements);
	}

	/**
	* Constructs a deque containing the elements of the specified
	* collection, in the order they are returned by the collection's
	* iterator. (The first element returned by the collection's
	* iterator becomes the first element, or <i>front</i> of the
	* deque.)
	*
	* @param c the collection whose elements are to be placed into the deque
	* @throws NullPointerException if the specified collection is null
	*/
	public ArrayDeque(Collection<? extends E> c) {
	allocateElements(c.size());
	addAll(c);
	}

	// The main insertion and extraction methods are addFirst,
	// addLast, pollFirst, pollLast. The other methods are defined in
	// terms of these.

	/**
	* Inserts the specified element at the front of this deque.
	*
	* @param e the element to add
	* @throws NullPointerException if the specified element is null
	*/
	public void addFirst(E e) {
	if (e == null)
	throw new NullPointerException();
	elements[head = (head - 1) & (elements.length - 1)] = e;
	if (head == tail)
	doubleCapacity();
	}

	/**
	* Inserts the specified element at the end of this deque.
	*
	* <p>This method is equivalent to {@link #add}.
	*
	* @param e the element to add
	* @throws NullPointerException if the specified element is null
	*/
	public void addLast(E e) {
	if (e == null)
	throw new NullPointerException();
	elements[tail] = e;
	if ( (tail = (tail + 1) & (elements.length - 1)) == head)
	doubleCapacity();
	}

	/**
	* Inserts the specified element at the front of this deque.
	*
	* @param e the element to add
	* @return {@code true} (as specified by {@link Deque#offerFirst})
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offerFirst(E e) {
	addFirst(e);
	return true;
	}

	/**
	* Inserts the specified element at the end of this deque.
	*
	* @param e the element to add
	* @return {@code true} (as specified by {@link Deque#offerLast})
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offerLast(E e) {
	addLast(e);
	return true;
	}

	/**
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E removeFirst() {
	E x = pollFirst();
	if (x == null)
	throw new NoSuchElementException();
	return x;
	}

	/**
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E removeLast() {
	E x = pollLast();
	if (x == null)
	throw new NoSuchElementException();
	return x;
	}

	public E pollFirst() {
	int h = head;
	@SuppressWarnings("unchecked")
	E result = (E) elements[h];
	// Element is null if deque empty
	if (result == null)
	return null;
	elements[h] = null; // Must null out slot
	head = (h + 1) & (elements.length - 1);
	return result;
	}

	public E pollLast() {
	int t = (tail - 1) & (elements.length - 1);
	@SuppressWarnings("unchecked")
	E result = (E) elements[t];
	if (result == null)
	return null;
	elements[t] = null;
	tail = t;
	return result;
	}

	/**
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E getFirst() {
	@SuppressWarnings("unchecked")
	E result = (E) elements[head];
	if (result == null)
	throw new NoSuchElementException();
	return result;
	}

	/**
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E getLast() {
	@SuppressWarnings("unchecked")
	E result = (E) elements[(tail - 1) & (elements.length - 1)];
	if (result == null)
	throw new NoSuchElementException();
	return result;
	}

	@SuppressWarnings("unchecked")
	public E peekFirst() {
	// elements[head] is null if deque empty
	return (E) elements[head];
	}

	@SuppressWarnings("unchecked")
	public E peekLast() {
	return (E) elements[(tail - 1) & (elements.length - 1)];
	}

	/**
	* Removes the first occurrence of the specified element in this
	* deque (when traversing the deque from head to tail).
	* If the deque does not contain the element, it is unchanged.
	* More formally, removes the first element {@code e} such that
	* {@code o.equals(e)} (if such an element exists).
	* Returns {@code true} if this deque contained the specified element
	* (or equivalently, if this deque changed as a result of the call).
	*
	* @param o element to be removed from this deque, if present
	* @return {@code true} if the deque contained the specified element
	*/
	public boolean removeFirstOccurrence(Object o) {
	if (o == null)
	return false;
	int mask = elements.length - 1;
	int i = head;
	Object x;
	while ( (x = elements[i]) != null) {
	if (o.equals(x)) {
	delete(i);
	return true;
	}
	i = (i + 1) & mask;
	}
	return false;
	}

	/**
	* Removes the last occurrence of the specified element in this
	* deque (when traversing the deque from head to tail).
	* If the deque does not contain the element, it is unchanged.
	* More formally, removes the last element {@code e} such that
	* {@code o.equals(e)} (if such an element exists).
	* Returns {@code true} if this deque contained the specified element
	* (or equivalently, if this deque changed as a result of the call).
	*
	* @param o element to be removed from this deque, if present
	* @return {@code true} if the deque contained the specified element
	*/
	public boolean removeLastOccurrence(Object o) {
	if (o == null)
	return false;
	int mask = elements.length - 1;
	int i = (tail - 1) & mask;
	Object x;
	while ( (x = elements[i]) != null) {
	if (o.equals(x)) {
	delete(i);
	return true;
	}
	i = (i - 1) & mask;
	}
	return false;
	}

	// * Queue methods *

	/**
	* Inserts the specified element at the end of this deque.
	*
	* <p>This method is equivalent to {@link #addLast}.
	*
	* @param e the element to add
	* @return {@code true} (as specified by {@link Collection#add})
	* @throws NullPointerException if the specified element is null
	*/
	public boolean add(E e) {
	addLast(e);
	return true;
	}

	/**
	* Inserts the specified element at the end of this deque.
	*
	* <p>This method is equivalent to {@link #offerLast}.
	*
	* @param e the element to add
	* @return {@code true} (as specified by {@link Queue#offer})
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offer(E e) {
	return offerLast(e);
	}

	/**
	* Retrieves and removes the head of the queue represented by this deque.
	*
	* This method differs from {@link #poll poll} only in that it throws an
	* exception if this deque is empty.
	*
	* <p>This method is equivalent to {@link #removeFirst}.
	*
	* @return the head of the queue represented by this deque
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E remove() {
	return removeFirst();
	}

	/**
	* Retrieves and removes the head of the queue represented by this deque
	* (in other words, the first element of this deque), or returns
	* {@code null} if this deque is empty.
	*
	* <p>This method is equivalent to {@link #pollFirst}.
	*
	* @return the head of the queue represented by this deque, or
	* {@code null} if this deque is empty
	*/
	public E poll() {
	return pollFirst();
	}

	/**
	* Retrieves, but does not remove, the head of the queue represented by
	* this deque. This method differs from {@link #peek peek} only in
	* that it throws an exception if this deque is empty.
	*
	* <p>This method is equivalent to {@link #getFirst}.
	*
	* @return the head of the queue represented by this deque
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E element() {
	return getFirst();
	}

	/**
	* Retrieves, but does not remove, the head of the queue represented by
	* this deque, or returns {@code null} if this deque is empty.
	*
	* <p>This method is equivalent to {@link #peekFirst}.
	*
	* @return the head of the queue represented by this deque, or
	* {@code null} if this deque is empty
	*/
	public E peek() {
	return peekFirst();
	}

	// * Stack methods *

	/**
	* Pushes an element onto the stack represented by this deque. In other
	* words, inserts the element at the front of this deque.
	*
	* <p>This method is equivalent to {@link #addFirst}.
	*
	* @param e the element to push
	* @throws NullPointerException if the specified element is null
	*/
	public void push(E e) {
	addFirst(e);
	}

	/**
	* Pops an element from the stack represented by this deque. In other
	* words, removes and returns the first element of this deque.
	*
	* <p>This method is equivalent to {@link #removeFirst()}.
	*
	* @return the element at the front of this deque (which is the top
	* of the stack represented by this deque)
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E pop() {
	return removeFirst();
	}

	private void checkInvariants() {
	assert elements[tail] == null;
	assert head == tail ? elements[head] == null :
	(elements[head] != null &&
	elements[(tail - 1) & (elements.length - 1)] != null);
	assert elements[(head - 1) & (elements.length - 1)] == null;
	}

	/**
	* Removes the element at the specified position in the elements array,
	* adjusting head and tail as necessary. This can result in motion of
	* elements backwards or forwards in the array.
	*
	* <p>This method is called delete rather than remove to emphasize
	* that its semantics differ from those of {@link List#remove(int)}.
	*
	* @return true if elements moved backwards
	*/
	private boolean delete(int i) {
	checkInvariants();
	final Object[] elements = this.elements;
	final int mask = elements.length - 1;
	final int h = head;
	final int t = tail;
	final int front = (i - h) & mask;
	final int back = (t - i) & mask;

	// Invariant: head <= i < tail mod circularity
	if (front >= ((t - h) & mask))
	throw new ConcurrentModificationException();

	// Optimize for least element motion
	if (front < back) {
	if (h <= i) {
	System.arraycopy(elements, h, elements, h + 1, front);
	} else { // Wrap around
	System.arraycopy(elements, 0, elements, 1, i);
	elements[0] = elements[mask];
	System.arraycopy(elements, h, elements, h + 1, mask - h);
	}
	elements[h] = null;
	head = (h + 1) & mask;
	return false;
	} else {
	if (i < t) { // Copy the null tail as well
	System.arraycopy(elements, i + 1, elements, i, back);
	tail = t - 1;
	} else { // Wrap around
	System.arraycopy(elements, i + 1, elements, i, mask - i);
	elements[mask] = elements[0];
	System.arraycopy(elements, 1, elements, 0, t);
	tail = (t - 1) & mask;
	}
	return true;
	}
	}

	// * Collection Methods *

	/**
	* Returns the number of elements in this deque.
	*
	* @return the number of elements in this deque
	*/
	public int size() {
	return (tail - head) & (elements.length - 1);
	}

	/**
	* Returns {@code true} if this deque contains no elements.
	*
	* @return {@code true} if this deque contains no elements
	*/
	public boolean isEmpty() {
	return head == tail;
	}

	/**
	* Returns an iterator over the elements in this deque. The elements
	* will be ordered from first (head) to last (tail). This is the same
	* order that elements would be dequeued (via successive calls to
	* {@link #remove} or popped (via successive calls to {@link #pop}).
	*
	* @return an iterator over the elements in this deque
	*/
	public Iterator<E> iterator() {
	return new DeqIterator();
	}

	public Iterator<E> descendingIterator() {
	return new DescendingIterator();
	}

	private class DeqIterator implements Iterator<E> {
	/**
	* Index of element to be returned by subsequent call to next.
	*/
	private int cursor = head;

	/**
	* Tail recorded at construction (also in remove), to stop
	* iterator and also to check for comodification.
	*/
	private int fence = tail;

	/**
	* Index of element returned by most recent call to next.
	* Reset to -1 if element is deleted by a call to remove.
	*/
	private int lastRet = -1;

	public boolean hasNext() {
	return cursor != fence;
	}

	public E next() {
	if (cursor == fence)
	throw new NoSuchElementException();
	@SuppressWarnings("unchecked")
	E result = (E) elements[cursor];
	// This check doesn't catch all possible comodifications,
	// but does catch the ones that corrupt traversal
	if (tail != fence \|\| result == null)
	throw new ConcurrentModificationException();
	lastRet = cursor;
	cursor = (cursor + 1) & (elements.length - 1);
	return result;
	}

	public void remove() {
	if (lastRet < 0)
	throw new IllegalStateException();
	if (delete(lastRet)) { // if left-shifted, undo increment in next()
	cursor = (cursor - 1) & (elements.length - 1);
	fence = tail;
	}
	lastRet = -1;
	}

	public void forEachRemaining(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	Object[] a = elements;
	int m = a.length - 1, f = fence, i = cursor;
	cursor = f;
	while (i != f) {
	@SuppressWarnings("unchecked") E e = (E)a[i];
	i = (i + 1) & m;
	if (e == null)
	throw new ConcurrentModificationException();
	action.accept(e);
	}
	}
	}

	private class DescendingIterator implements Iterator<E> {
	/*
	* This class is nearly a mirror-image of DeqIterator, using
	* tail instead of head for initial cursor, and head instead of
	* tail for fence.
	*/
	private int cursor = tail;
	private int fence = head;
	private int lastRet = -1;

	public boolean hasNext() {
	return cursor != fence;
	}

	public E next() {
	if (cursor == fence)
	throw new NoSuchElementException();
	cursor = (cursor - 1) & (elements.length - 1);
	@SuppressWarnings("unchecked")
	E result = (E) elements[cursor];
	if (head != fence \|\| result == null)
	throw new ConcurrentModificationException();
	lastRet = cursor;
	return result;
	}

	public void remove() {
	if (lastRet < 0)
	throw new IllegalStateException();
	if (!delete(lastRet)) {
	cursor = (cursor + 1) & (elements.length - 1);
	fence = head;
	}
	lastRet = -1;
	}
	}

	/**
	* Returns {@code true} if this deque contains the specified element.
	* More formally, returns {@code true} if and only if this deque contains
	* at least one element {@code e} such that {@code o.equals(e)}.
	*
	* @param o object to be checked for containment in this deque
	* @return {@code true} if this deque contains the specified element
	*/
	public boolean contains(Object o) {
	if (o == null)
	return false;
	int mask = elements.length - 1;
	int i = head;
	Object x;
	while ( (x = elements[i]) != null) {
	if (o.equals(x))
	return true;
	i = (i + 1) & mask;
	}
	return false;
	}

	/**
	* Removes a single instance of the specified element from this deque.
	* If the deque does not contain the element, it is unchanged.
	* More formally, removes the first element {@code e} such that
	* {@code o.equals(e)} (if such an element exists).
	* Returns {@code true} if this deque contained the specified element
	* (or equivalently, if this deque changed as a result of the call).
	*
	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
	*
	* @param o element to be removed from this deque, if present
	* @return {@code true} if this deque contained the specified element
	*/
	public boolean remove(Object o) {
	return removeFirstOccurrence(o);
	}

	/**
	* Removes all of the elements from this deque.
	* The deque will be empty after this call returns.
	*/
	public void clear() {
	int h = head;
	int t = tail;
	if (h != t) { // clear all cells
	head = tail = 0;
	int i = h;
	int mask = elements.length - 1;
	do {
	elements[i] = null;
	i = (i + 1) & mask;
	} while (i != t);
	}
	}

	/**
	* Returns an array containing all of the elements in this deque
	* in proper sequence (from first to last element).
	*
	* <p>The returned array will be "safe" in that no references to it are
	* maintained by this deque. (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 deque
	*/
	public Object[] toArray() {
	return copyElements(new Object[size()]);
	}

	/**
	* Returns an array containing all of the elements in this deque in
	* proper sequence (from first to last element); the runtime type of the
	* returned array is that of the specified array. If the deque 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 deque.
	*
	* <p>If this deque fits in the specified array with room to spare
	* (i.e., the array has more elements than this deque), the element in
	* the array immediately following the end of the deque 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 deque known to contain only strings.
	* The following code can be used to dump the deque 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 deque 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 deque
	* @throws ArrayStoreException if the runtime type of the specified array
	* is not a supertype of the runtime type of every element in
	* this deque
	* @throws NullPointerException if the specified array is null
	*/
	@SuppressWarnings("unchecked")
	public <T> T[] toArray(T[] a) {
	int size = size();
	if (a.length < size)
	a = (T[])java.lang.reflect.Array.newInstance(
	a.getClass().getComponentType(), size);
	copyElements(a);
	if (a.length > size)
	a[size] = null;
	return a;
	}

	// * Object methods *

	/**
	* Returns a copy of this deque.
	*
	* @return a copy of this deque
	*/
	public ArrayDeque<E> clone() {
	try {
	@SuppressWarnings("unchecked")
	ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
	result.elements = Arrays.copyOf(elements, elements.length);
	return result;
	} catch (CloneNotSupportedException e) {
	throw new AssertionError();
	}
	}

	private static final long serialVersionUID = 2340985798034038923L;

	/**
	* Saves this deque to a stream (that is, serializes it).
	*
	* @serialData The current size ({@code int}) of the deque,
	* followed by all of its elements (each an object reference) in
	* first-to-last order.
	*/
	private void writeObject(java.io.ObjectOutputStream s)
	throws java.io.IOException {
	s.defaultWriteObject();

	// Write out size
	s.writeInt(size());

	// Write out elements in order.
	int mask = elements.length - 1;
	for (int i = head; i != tail; i = (i + 1) & mask)
	s.writeObject(elements[i]);
	}

	/**
	* Reconstitutes this deque from a stream (that is, deserializes it).
	*/
	private void readObject(java.io.ObjectInputStream s)
	throws java.io.IOException, ClassNotFoundException {
	s.defaultReadObject();

	// Read in size and allocate array
	int size = s.readInt();
	int capacity = calculateSize(size);
	SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, capacity);
	allocateElements(size);
	head = 0;
	tail = size;

	// Read in all elements in the proper order.
	for (int i = 0; i < size; i++)
	elements[i] = s.readObject();
	}

	/**
	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
	* deque.
	*
	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
	* {@link Spliterator#NONNULL}. Overriding implementations should document
	* the reporting of additional characteristic values.
	*
	* @return a {@code Spliterator} over the elements in this deque
	* @since 1.8
	*/
	public Spliterator<E> spliterator() {
	return new DeqSpliterator<E>(this, -1, -1);
	}

	static final class DeqSpliterator<E> implements Spliterator<E> {
	private final ArrayDeque<E> deq;
	private int fence; // -1 until first use
	private int index; // current index, modified on traverse/split

	/** Creates new spliterator covering the given array and range */
	DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) {
	this.deq = deq;
	this.index = origin;
	this.fence = fence;
	}

	private int getFence() { // force initialization
	int t;
	if ((t = fence) < 0) {
	t = fence = deq.tail;
	index = deq.head;
	}
	return t;
	}

	public DeqSpliterator<E> trySplit() {
	int t = getFence(), h = index, n = deq.elements.length;
	if (h != t && ((h + 1) & (n - 1)) != t) {
	if (h > t)
	t += n;
	int m = ((h + t) >>> 1) & (n - 1);
	return new DeqSpliterator<>(deq, h, index = m);
	}
	return null;
	}

	public void forEachRemaining(Consumer<? super E> consumer) {
	if (consumer == null)
	throw new NullPointerException();
	Object[] a = deq.elements;
	int m = a.length - 1, f = getFence(), i = index;
	index = f;
	while (i != f) {
	@SuppressWarnings("unchecked") E e = (E)a[i];
	i = (i + 1) & m;
	if (e == null)
	throw new ConcurrentModificationException();
	consumer.accept(e);
	}
	}

	public boolean tryAdvance(Consumer<? super E> consumer) {
	if (consumer == null)
	throw new NullPointerException();
	Object[] a = deq.elements;
	int m = a.length - 1, f = getFence(), i = index;
	if (i != fence) {
	@SuppressWarnings("unchecked") E e = (E)a[i];
	index = (i + 1) & m;
	if (e == null)
	throw new ConcurrentModificationException();
	consumer.accept(e);
	return true;
	}
	return false;
	}

	public long estimateSize() {
	int n = getFence() - index;
	if (n < 0)
	n += deq.elements.length;
	return (long) n;
	}

	@Override
	public int characteristics() {
	return Spliterator.ORDERED \| Spliterator.SIZED \|
	Spliterator.NONNULL \| Spliterator.SUBSIZED;
	}
	}

	}

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