/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.collection.ArrayDeque;

/**
 * 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
 * @param !E the type of elements held in this collection
 */
// class ArrayDeque(E) : AbstractCollection!E
//                            , 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.
//      */
//     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.
//      */
//     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)).
//      */
//     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 ******

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

//     /**
//      * 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.
//      */
//     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
//      */
//     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
//      */
//     ArrayDeque(Collection<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
//      */
//     void addFirst(E e) {
//         if (e is 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
//      */
//     void addLast(E e) {
//         if (e is 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
//      */
//     bool 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
//      */
//     bool offerLast(E e) {
//         addLast(e);
//         return true;
//     }

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

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

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

//     E pollLast() {
//         int t = (tail - 1) & (elements.length - 1);
//     
//         E result = (E) elements[t];
//         if (result is null)
//             return null;
//         elements[t] = null;
//         tail = t;
//         return result;
//     }

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

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

// 
//     E peekFirst() {
//         // elements[head] is null if deque empty
//         return (E) elements[head];
//     }

// 
//     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
//      */
//     bool removeFirstOccurrence(Object o) {
//         if (o is null)
//             return false;
//         int mask = elements.length - 1;
//         int i = head;
//         Object x;
//         while ( (x = elements[i]) !is 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
//      */
//     bool removeLastOccurrence(Object o) {
//         if (o is null)
//             return false;
//         int mask = elements.length - 1;
//         int i = (tail - 1) & mask;
//         Object x;
//         while ( (x = elements[i]) !is 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
//      */
//     bool 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
//      */
//     bool 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}
//      */
//     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
//      */
//     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}
//      */
//     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
//      */
//     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
//      */
//     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}
//      */
//     E pop() {
//         return removeFirst();
//     }

//     private void checkInvariants() {
//         assert elements[tail] is null;
//         assert head == tail ? elements[head] is null :
//             (elements[head] !is null &&
//              elements[(tail - 1) & (elements.length - 1)] !is null);
//         assert elements[(head - 1) & (elements.length - 1)] is 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 bool 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
//      */
//     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
//      */
//     bool 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
//      */
//     Iterator!E iterator() {
//         return new DeqIterator();
//     }

//     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;

//         bool hasNext() {
//             return cursor != fence;
//         }

//         E next() {
//             if (cursor == fence)
//                 throw new NoSuchElementException();
//         
//             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 is null)
//                 throw new ConcurrentModificationException();
//             lastRet = cursor;
//             cursor = (cursor + 1) & (elements.length - 1);
//             return result;
//         }

//         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;
//         }

//         void forEachRemaining(Consumer<E> action) {
//             Objects.requireNonNull(action);
//             Object[] a = elements;
//             int m = a.length - 1, f = fence, i = cursor;
//             cursor = f;
//             while (i != f) {
//             E e = (E)a[i];
//                 i = (i + 1) & m;
//                 if (e is 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;

//         bool hasNext() {
//             return cursor != fence;
//         }

//         E next() {
//             if (cursor == fence)
//                 throw new NoSuchElementException();
//             cursor = (cursor - 1) & (elements.length - 1);
//         
//             E result = (E) elements[cursor];
//             if (head != fence || result is null)
//                 throw new ConcurrentModificationException();
//             lastRet = cursor;
//             return result;
//         }

//         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
//      */
//     bool contains(Object o) {
//         if (o is null)
//             return false;
//         int mask = elements.length - 1;
//         int i = head;
//         Object x;
//         while ( (x = elements[i]) !is 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
//      */
//     bool remove(Object o) {
//         return removeFirstOccurrence(o);
//     }

//     /**
//      * Removes all of the elements from this deque.
//      * The deque will be empty after this call returns.
//      */
//     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
//      */
//     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
//      */
// 
//     !(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
//      */
//     ArrayDeque!E clone() {
//         try {
//         
//             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();
//         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
//      */
//     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;
//         }

//         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;
//         }

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

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

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

//         override
//         int characteristics() {
//             return Spliterator.ORDERED | Spliterator.SIZED |
//                 Spliterator.NONNULL | Spliterator.SUBSIZED;
//         }
//     }

// }