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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 java.util.function.Predicate;
	import java.util.function.UnaryOperator;
	import jdk.internal.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 {@link #iterator() iterator}
	* method are <em>fail-fast</em>: 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}/java.base/java/util/package-summary.html#CollectionsFramework">
	* Java Collections Framework</a>.
	*
	* @author Josh Bloch and Doug Lea
	* @param <E> the type of elements held in this deque
	* @since 1.6
	*/
	public class ArrayDeque<E> extends AbstractCollection<E>
	implements Deque<E>, Cloneable, Serializable
	{
	/*
	* VMs excel at optimizing simple array loops where indices are
	* incrementing or decrementing over a valid slice, e.g.
	*
	* for (int i = start; i < end; i++) ... elements[i]
	*
	* Because in a circular array, elements are in general stored in
	* two disjoint such slices, we help the VM by writing unusual
	* nested loops for all traversals over the elements. Having only
	* one hot inner loop body instead of two or three eases human
	* maintenance and encourages VM loop inlining into the caller.
	*/

	/**
	* The array in which the elements of the deque are stored.
	* All array cells not holding deque elements are always null.
	* The array always has at least one null slot (at tail).
	*/
	transient Object[] elements;

	/**
	* 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 0 <= head < elements.length 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));
	* elements[tail] is always null.
	*/
	transient int tail;

	/**
	* 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 this deque by at least the given amount.
	*
	* @param needed the required minimum extra capacity; must be positive
	*/
	private void grow(int needed) {
	// overflow-conscious code
	final int oldCapacity = elements.length;
	int newCapacity;
	// Double capacity if small; else grow by 50%
	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
	if (jump < needed
	\|\| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
	newCapacity = newCapacity(needed, jump);
	final Object[] es = elements = Arrays.copyOf(elements, newCapacity);
	// Exceptionally, here tail == head needs to be disambiguated
	if (tail < head \|\| (tail == head && es[head] != null)) {
	// wrap around; slide first leg forward to end of array
	int newSpace = newCapacity - oldCapacity;
	System.arraycopy(es, head,
	es, head + newSpace,
	oldCapacity - head);
	for (int i = head, to = (head += newSpace); i < to; i++)
	es[i] = null;
	}
	}

	/** Capacity calculation for edge conditions, especially overflow. */
	private int newCapacity(int needed, int jump) {
	final int oldCapacity = elements.length, minCapacity;
	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
	if (minCapacity < 0)
	throw new IllegalStateException("Sorry, deque too big");
	return Integer.MAX_VALUE;
	}
	if (needed > jump)
	return minCapacity;
	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
	? oldCapacity + jump
	: MAX_ARRAY_SIZE;
	}

	/**
	* 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) {
	elements =
	new Object[(numElements < 1) ? 1 :
	(numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
	numElements + 1];
	}

	/**
	* 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) {
	this(c.size());
	copyElements(c);
	}

	/**
	* Circularly increments i, mod modulus.
	* Precondition and postcondition: 0 <= i < modulus.
	*/
	static final int inc(int i, int modulus) {
	if (++i >= modulus) i = 0;
	return i;
	}

	/**
	* Circularly decrements i, mod modulus.
	* Precondition and postcondition: 0 <= i < modulus.
	*/
	static final int dec(int i, int modulus) {
	if (--i < 0) i = modulus - 1;
	return i;
	}

	/**
	* Circularly adds the given distance to index i, mod modulus.
	* Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
	* @return index 0 <= i < modulus
	*/
	static final int inc(int i, int distance, int modulus) {
	if ((i += distance) - modulus >= 0) i -= modulus;
	return i;
	}

	/**
	* Subtracts j from i, mod modulus.
	* Index i must be logically ahead of index j.
	* Precondition: 0 <= i < modulus, 0 <= j < modulus.
	* @return the "circular distance" from j to i; corner case i == j
	* is disambiguated to "empty", returning 0.
	*/
	static final int sub(int i, int j, int modulus) {
	if ((i -= j) < 0) i += modulus;
	return i;
	}

	/**
	* Returns element at array index i.
	* This is a slight abuse of generics, accepted by javac.
	*/
	@SuppressWarnings("unchecked")
	static final <E> E elementAt(Object[] es, int i) {
	return (E) es[i];
	}

	/**
	* A version of elementAt that checks for null elements.
	* This check doesn't catch all possible comodifications,
	* but does catch ones that corrupt traversal.
	*/
	static final <E> E nonNullElementAt(Object[] es, int i) {
	@SuppressWarnings("unchecked") E e = (E) es[i];
	if (e == null)
	throw new ConcurrentModificationException();
	return e;
	}

	// 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();
	final Object[] es = elements;
	es[head = dec(head, es.length)] = e;
	if (head == tail)
	grow(1);
	}

	/**
	* 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();
	final Object[] es = elements;
	es[tail] = e;
	if (head == (tail = inc(tail, es.length)))
	grow(1);
	}

	/**
	* Adds all of the elements in the specified collection at the end
	* of this deque, as if by calling {@link #addLast} on each one,
	* in the order that they are returned by the collection's iterator.
	*
	* @param c the elements to be inserted into this deque
	* @return {@code true} if this deque changed as a result of the call
	* @throws NullPointerException if the specified collection or any
	* of its elements are null
	*/
	public boolean addAll(Collection<? extends E> c) {
	final int s, needed;
	if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
	grow(needed);
	copyElements(c);
	return size() > s;
	}

	private void copyElements(Collection<? extends E> c) {
	c.forEach(this::addLast);
	}

	/**
	* 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 e = pollFirst();
	if (e == null)
	throw new NoSuchElementException();
	return e;
	}

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

	public E pollFirst() {
	final Object[] es;
	final int h;
	E e = elementAt(es = elements, h = head);
	if (e != null) {
	es[h] = null;
	head = inc(h, es.length);
	}
	return e;
	}

	public E pollLast() {
	final Object[] es;
	final int t;
	E e = elementAt(es = elements, t = dec(tail, es.length));
	if (e != null)
	es[tail = t] = null;
	return e;
	}

	/**
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E getFirst() {
	E e = elementAt(elements, head);
	if (e == null)
	throw new NoSuchElementException();
	return e;
	}

	/**
	* @throws NoSuchElementException {@inheritDoc}
	*/
	public E getLast() {
	final Object[] es = elements;
	E e = elementAt(es, dec(tail, es.length));
	if (e == null)
	throw new NoSuchElementException();
	return e;
	}

	public E peekFirst() {
	return elementAt(elements, head);
	}

	public E peekLast() {
	final Object[] es;
	return elementAt(es = elements, dec(tail, es.length));
	}

	/**
	* 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) {
	final Object[] es = elements;
	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	if (o.equals(es[i])) {
	delete(i);
	return true;
	}
	if (to == end) break;
	}
	}
	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) {
	final Object[] es = elements;
	for (int i = tail, end = head, to = (i >= end) ? end : 0;
	; i = es.length, to = end) {
	for (i--; i > to - 1; i--)
	if (o.equals(es[i])) {
	delete(i);
	return true;
	}
	if (to == end) break;
	}
	}
	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();
	}

	/**
	* Removes the element at the specified position in the elements array.
	* This can result in forward or backwards motion of array elements.
	* We optimize for least element motion.
	*
	* <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 near tail moved backwards
	*/
	boolean delete(int i) {
	final Object[] es = elements;
	final int capacity = es.length;
	final int h, t;
	// number of elements before to-be-deleted elt
	final int front = sub(i, h = head, capacity);
	// number of elements after to-be-deleted elt
	final int back = sub(t = tail, i, capacity) - 1;
	if (front < back) {
	// move front elements forwards
	if (h <= i) {
	System.arraycopy(es, h, es, h + 1, front);
	} else { // Wrap around
	System.arraycopy(es, 0, es, 1, i);
	es[0] = es[capacity - 1];
	System.arraycopy(es, h, es, h + 1, front - (i + 1));
	}
	es[h] = null;
	head = inc(h, capacity);
	return false;
	} else {
	// move back elements backwards
	tail = dec(t, capacity);
	if (i <= tail) {
	System.arraycopy(es, i + 1, es, i, back);
	} else { // Wrap around
	System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
	es[capacity - 1] = es[0];
	System.arraycopy(es, 1, es, 0, t - 1);
	}
	es[tail] = null;
	return true;
	}
	}

	// * Collection Methods *

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

	/**
	* 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. */
	int cursor;

	/** Number of elements yet to be returned. */
	int remaining = size();

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

	DeqIterator() { cursor = head; }

	public final boolean hasNext() {
	return remaining > 0;
	}

	public E next() {
	if (remaining <= 0)
	throw new NoSuchElementException();
	final Object[] es = elements;
	E e = nonNullElementAt(es, cursor);
	cursor = inc(lastRet = cursor, es.length);
	remaining--;
	return e;
	}

	void postDelete(boolean leftShifted) {
	if (leftShifted)
	cursor = dec(cursor, elements.length);
	}

	public final void remove() {
	if (lastRet < 0)
	throw new IllegalStateException();
	postDelete(delete(lastRet));
	lastRet = -1;
	}

	public void forEachRemaining(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	int r;
	if ((r = remaining) <= 0)
	return;
	remaining = 0;
	final Object[] es = elements;
	if (es[cursor] == null \|\| sub(tail, cursor, es.length) != r)
	throw new ConcurrentModificationException();
	for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	action.accept(elementAt(es, i));
	if (to == end) {
	if (end != tail)
	throw new ConcurrentModificationException();
	lastRet = dec(end, es.length);
	break;
	}
	}
	}
	}

	private class DescendingIterator extends DeqIterator {
	DescendingIterator() { cursor = dec(tail, elements.length); }

	public final E next() {
	if (remaining <= 0)
	throw new NoSuchElementException();
	final Object[] es = elements;
	E e = nonNullElementAt(es, cursor);
	cursor = dec(lastRet = cursor, es.length);
	remaining--;
	return e;
	}

	void postDelete(boolean leftShifted) {
	if (!leftShifted)
	cursor = inc(cursor, elements.length);
	}

	public final void forEachRemaining(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	int r;
	if ((r = remaining) <= 0)
	return;
	remaining = 0;
	final Object[] es = elements;
	if (es[cursor] == null \|\| sub(cursor, head, es.length) + 1 != r)
	throw new ConcurrentModificationException();
	for (int i = cursor, end = head, to = (i >= end) ? end : 0;
	; i = es.length - 1, to = end) {
	// hotspot generates faster code than for: i >= to !
	for (; i > to - 1; i--)
	action.accept(elementAt(es, i));
	if (to == end) {
	if (end != head)
	throw new ConcurrentModificationException();
	lastRet = end;
	break;
	}
	}
	}
	}

	/**
	* 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();
	}

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

	/** Constructs late-binding spliterator over all elements. */
	DeqSpliterator() {
	this.fence = -1;
	}

	/** Constructs spliterator over the given range. */
	DeqSpliterator(int origin, int fence) {
	// assert 0 <= origin && origin < elements.length;
	// assert 0 <= fence && fence < elements.length;
	this.cursor = origin;
	this.fence = fence;
	}

	/** Ensures late-binding initialization; then returns fence. */
	private int getFence() { // force initialization
	int t;
	if ((t = fence) < 0) {
	t = fence = tail;
	cursor = head;
	}
	return t;
	}

	public DeqSpliterator trySplit() {
	final Object[] es = elements;
	final int i, n;
	return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
	? null
	: new DeqSpliterator(i, cursor = inc(i, n, es.length));
	}

	public void forEachRemaining(Consumer<? super E> action) {
	if (action == null)
	throw new NullPointerException();
	final int end = getFence(), cursor = this.cursor;
	final Object[] es = elements;
	if (cursor != end) {
	this.cursor = end;
	// null check at both ends of range is sufficient
	if (es[cursor] == null \|\| es[dec(end, es.length)] == null)
	throw new ConcurrentModificationException();
	for (int i = cursor, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	action.accept(elementAt(es, i));
	if (to == end) break;
	}
	}
	}

	public boolean tryAdvance(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	final Object[] es = elements;
	if (fence < 0) { fence = tail; cursor = head; } // late-binding
	final int i;
	if ((i = cursor) == fence)
	return false;
	E e = nonNullElementAt(es, i);
	cursor = inc(i, es.length);
	action.accept(e);
	return true;
	}

	public long estimateSize() {
	return sub(getFence(), cursor, elements.length);
	}

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

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public void forEach(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	final Object[] es = elements;
	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	action.accept(elementAt(es, i));
	if (to == end) {
	if (end != tail) throw new ConcurrentModificationException();
	break;
	}
	}
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean removeIf(Predicate<? super E> filter) {
	Objects.requireNonNull(filter);
	return bulkRemove(filter);
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean removeAll(Collection<?> c) {
	Objects.requireNonNull(c);
	return bulkRemove(e -> c.contains(e));
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean retainAll(Collection<?> c) {
	Objects.requireNonNull(c);
	return bulkRemove(e -> !c.contains(e));
	}

	/** Implementation of bulk remove methods. */
	private boolean bulkRemove(Predicate<? super E> filter) {
	final Object[] es = elements;
	// Optimize for initial run of survivors
	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	if (filter.test(elementAt(es, i)))
	return bulkRemoveModified(filter, i);
	if (to == end) {
	if (end != tail) throw new ConcurrentModificationException();
	break;
	}
	}
	return false;
	}

	// A tiny bit set implementation

	private static long[] nBits(int n) {
	return new long[((n - 1) >> 6) + 1];
	}
	private static void setBit(long[] bits, int i) {
	bits[i >> 6] \|= 1L << i;
	}
	private static boolean isClear(long[] bits, int i) {
	return (bits[i >> 6] & (1L << i)) == 0;
	}

	/**
	* Helper for bulkRemove, in case of at least one deletion.
	* Tolerate predicates that reentrantly access the collection for
	* read (but writers still get CME), so traverse once to find
	* elements to delete, a second pass to physically expunge.
	*
	* @param beg valid index of first element to be deleted
	*/
	private boolean bulkRemoveModified(
	Predicate<? super E> filter, final int beg) {
	final Object[] es = elements;
	final int capacity = es.length;
	final int end = tail;
	final long[] deathRow = nBits(sub(end, beg, capacity));
	deathRow[0] = 1L; // set bit 0
	for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
	; i = 0, to = end, k -= capacity) {
	for (; i < to; i++)
	if (filter.test(elementAt(es, i)))
	setBit(deathRow, i - k);
	if (to == end) break;
	}
	// a two-finger traversal, with hare i reading, tortoise w writing
	int w = beg;
	for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
	; w = 0) { // w rejoins i on second leg
	// In this loop, i and w are on the same leg, with i > w
	for (; i < to; i++)
	if (isClear(deathRow, i - k))
	es[w++] = es[i];
	if (to == end) break;
	// In this loop, w is on the first leg, i on the second
	for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++)
	if (isClear(deathRow, i - k))
	es[w++] = es[i];
	if (i >= to) {
	if (w == capacity) w = 0; // "corner" case
	break;
	}
	}
	if (end != tail) throw new ConcurrentModificationException();
	circularClear(es, tail = w, end);
	return true;
	}

	/**
	* 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) {
	final Object[] es = elements;
	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	if (o.equals(es[i]))
	return true;
	if (to == end) break;
	}
	}
	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() {
	circularClear(elements, head, tail);
	head = tail = 0;
	}

	/**
	* Nulls out slots starting at array index i, upto index end.
	* Condition i == end means "empty" - nothing to do.
	*/
	private static void circularClear(Object[] es, int i, int end) {
	// assert 0 <= i && i < es.length;
	// assert 0 <= end && end < es.length;
	for (int to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++) es[i] = null;
	if (to == end) break;
	}
	}

	/**
	* 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 toArray(Object[].class);
	}

	private <T> T[] toArray(Class<T[]> klazz) {
	final Object[] es = elements;
	final T[] a;
	final int head = this.head, tail = this.tail, end;
	if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
	// Uses null extension feature of copyOfRange
	a = Arrays.copyOfRange(es, head, end, klazz);
	} else {
	// integer overflow!
	a = Arrays.copyOfRange(es, 0, end - head, klazz);
	System.arraycopy(es, head, a, 0, es.length - head);
	}
	if (end != tail)
	System.arraycopy(es, 0, a, es.length - head, tail);
	return a;
	}

	/**
	* 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) {
	final int size;
	if ((size = size()) > a.length)
	return toArray((Class<T[]>) a.getClass());
	final Object[] es = elements;
	for (int i = head, j = 0, len = Math.min(size, es.length - i);
	; i = 0, len = tail) {
	System.arraycopy(es, i, a, j, len);
	if ((j += len) == size) break;
	}
	if (size < a.length)
	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).
	*
	* @param s the stream
	* @throws java.io.IOException if an I/O error occurs
	* @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.
	final Object[] es = elements;
	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
	; i = 0, to = end) {
	for (; i < to; i++)
	s.writeObject(es[i]);
	if (to == end) break;
	}
	}

	/**
	* Reconstitutes this deque from a stream (that is, deserializes it).
	* @param s the stream
	* @throws ClassNotFoundException if the class of a serialized object
	* could not be found
	* @throws java.io.IOException if an I/O error occurs
	*/
	private void readObject(java.io.ObjectInputStream s)
	throws java.io.IOException, ClassNotFoundException {
	s.defaultReadObject();

	// Read in size and allocate array
	int size = s.readInt();
	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size + 1);
	elements = new Object[size + 1];
	this.tail = size;

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

	/** debugging */
	void checkInvariants() {
	// Use head and tail fields with empty slot at tail strategy.
	// head == tail disambiguates to "empty".
	try {
	int capacity = elements.length;
	// assert 0 <= head && head < capacity;
	// assert 0 <= tail && tail < capacity;
	// assert capacity > 0;
	// assert size() < capacity;
	// assert head == tail \|\| elements[head] != null;
	// assert elements[tail] == null;
	// assert head == tail \|\| elements[dec(tail, capacity)] != null;
	} catch (Throwable t) {
	System.err.printf("head=%d tail=%d capacity=%d%n",
	head, tail, elements.length);
	System.err.printf("elements=%s%n",
	Arrays.toString(elements));
	throw t;
	}
	}

	}

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