/*
 * Written by Josh Bloch of Google Inc. and released to the public domain,
 * as explained at http://creativecommons.org/licenses/publicdomain.
 */

package org.emdev.utils.collections;

// BEGIN android-note
// removed link to collections framework docs
// END android-note

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Stack;

/**
 * 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 <tt>ArrayDeque</tt> 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 <tt>iterator</tt> 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 <tt>remove</tt> 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
 * <tt>ConcurrentModificationException</tt> 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.
 *
 * @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 Cloneable, Serializable {

    private final ThreadLocal<DeqIterator> iterators = new ThreadLocal<DeqIterator>();

    /**
     * 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.
     */
    private transient E[] 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 equal to tail if the deque is empty.
     */
    private 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)).
     */
    private 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 ******

    /**
     * Allocate empty array to hold the given number of elements.
     *
     * @param numElements
     *            the number of elements to hold
     */
    @SuppressWarnings("unchecked")
    private void allocateElements(final 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) {
                initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
            }
        }
        elements = (E[]) new Object[initialCapacity];
    }

    /**
     * Double the capacity of this deque. Call only when full, i.e.,
     * when head and tail have wrapped around to become equal.
     */
    @SuppressWarnings("unchecked")
    private void doubleCapacity() {
        assert head == tail;
        final int p = head;
        final int n = elements.length;
        final int r = n - p; // number of elements to the right of p
        final int newCapacity = n << 1;
        if (newCapacity < 0) {
            throw new IllegalStateException("Sorry, deque too big");
        }
        final Object[] a = new Object[newCapacity];
        System.arraycopy(elements, p, a, 0, r);
        System.arraycopy(elements, 0, a, r, p);
        elements = (E[]) 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(final T[] a) {
        if (head < tail) {
            System.arraycopy(elements, head, a, 0, size());
        } else if (head > tail) {
            final 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.
     */
    @SuppressWarnings("unchecked")
    public ArrayDeque() {
        elements = (E[]) 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(final 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(final 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(final 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(final 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 <tt>true</tt> (as specified by {@link Deque#offerFirst})
     * @throws NullPointerException
     *             if the specified element is null
     */
    public boolean offerFirst(final E e) {
        addFirst(e);
        return true;
    }

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

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

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

    public E pollFirst() {
        final int h = head;
        final E result = 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() {
        final int t = (tail - 1) & (elements.length - 1);
        final E result = elements[t];
        if (result == null) {
            return null;
        }
        elements[t] = null;
        tail = t;
        return result;
    }

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

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

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

    public E peekLast() {
        return 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 <tt>e</tt> such that <tt>o.equals(e)</tt> (if such an element exists).
     * Returns <tt>true</tt> 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 <tt>true</tt> if the deque contained the specified element
     */
    public boolean removeFirstOccurrence(final Object o) {
        if (o == null) {
            return false;
        }
        final int mask = elements.length - 1;
        int i = head;
        E 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 <tt>e</tt> such that <tt>o.equals(e)</tt> (if such an element exists).
     * Returns <tt>true</tt> 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 <tt>true</tt> if the deque contained the specified element
     */
    public boolean removeLastOccurrence(final Object o) {
        if (o == null) {
            return false;
        }
        final int mask = elements.length - 1;
        int i = (tail - 1) & mask;
        E 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 <tt>true</tt> (as specified by {@link Collection#add})
     * @throws NullPointerException
     *             if the specified element is null
     */
    @Override
    public boolean add(final 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 <tt>true</tt> (as specified by {@link Queue#offer})
     * @throws NullPointerException
     *             if the specified element is null
     */
    public boolean offer(final 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 <tt>null</tt> if this deque is empty.
     *
     * <p>
     * This method is equivalent to {@link #pollFirst}.
     *
     * @return the head of the queue represented by this deque, or <tt>null</tt> 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 <tt>null</tt> if this deque is empty.
     *
     * <p>
     * This method is equivalent to {@link #peekFirst}.
     *
     * @return the head of the queue represented by this deque, or <tt>null</tt> 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(final 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(final int i) {
        checkInvariants();
        final E[] 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
     */
    @Override
    public int size() {
        return (tail - head) & (elements.length - 1);
    }

    /**
     * Returns <tt>true</tt> if this deque contains no elements.
     *
     * @return <tt>true</tt> if this deque contains no elements
     */
    @Override
    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
     */
    @Override
    public TLIterator<E> iterator() {
        DeqIterator iter = iterators.get();
        if (iter == null) {
            iter = new DeqIterator();
            return iter;
        }
        iter.cursor = head;
        iter.fence = tail;
        iter.lastRet = -1;
        iterators.set(null);
        return iter;
    }

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

    private class DeqIterator implements TLIterator<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;

        private DeqIterator() {
        }

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

        @Override
        public E next() {
            if (cursor == fence) {
                throw new NoSuchElementException();
            }
            final E result = 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;
        }

        @Override
        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;
        }

        @Override
        public Iterator<E> iterator() {
            return this;
        }

        @Override
        public void release() {
            iterators.set(this);
        }
    }

    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;

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

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

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

    /**
     * Returns <tt>true</tt> if this deque contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this deque contains
     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
     *
     * @param o
     *            object to be checked for containment in this deque
     * @return <tt>true</tt> if this deque contains the specified element
     */
    @Override
    public boolean contains(final Object o) {
        if (o == null) {
            return false;
        }
        final int mask = elements.length - 1;
        int i = head;
        E 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 <tt>e</tt> such that <tt>o.equals(e)</tt> (if such an element exists).
     * Returns <tt>true</tt> 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}.
     *
     * @param o
     *            element to be removed from this deque, if present
     * @return <tt>true</tt> if this deque contained the specified element
     */
    @Override
    public boolean remove(final Object o) {
        return removeFirstOccurrence(o);
    }

    /**
     * Removes all of the elements from this deque.
     * The deque will be empty after this call returns.
     */
    @Override
    public void clear() {
        final int h = head;
        final int t = tail;
        if (h != t) { // clear all cells
            head = tail = 0;
            int i = h;
            final 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
     */
    @Override
    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 <tt>null</tt>.
     *
     * <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 <tt>x</tt> is a deque known to contain only strings. The following code can be used to dump the deque
     * into a newly allocated array of <tt>String</tt>:
     *
     * <pre>
     *
     *
     * String[] y = x.toArray(new String[0]);
     * </pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to <tt>toArray()</tt>.
     *
     * @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
     */
    @Override
    @SuppressWarnings("unchecked")
    public <T> T[] toArray(T[] a) {
        final 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
     */
    @Override
    @SuppressWarnings("unchecked")
    public ArrayDeque<E> clone() {
        try {
            final ArrayDeque<E> result = (ArrayDeque<E>) super.clone();

            result.elements = (E[]) Array.newInstance(elements.getClass().getComponentType(), elements.length);
            System.arraycopy(elements, 0, result, 0, elements.length);

            return result;

        } catch (final CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }

    /**
     * Appease the serialization gods.
     */
    private static final long serialVersionUID = 2340985798034038923L;

    /**
     * Serialize this deque.
     *
     * @serialData The current size (<tt>int</tt>) of the deque,
     *             followed by all of its elements (each an object reference) in
     *             first-to-last order.
     */
    private void writeObject(final ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();

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

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

    /**
     * Deserialize this deque.
     */
    @SuppressWarnings("unchecked")
    private void readObject(final ObjectInputStream s) throws IOException, ClassNotFoundException {
        s.defaultReadObject();

        // Read in size and allocate array
        final 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] = (E) s.readObject();
        }
    }
}
