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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

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 * You should have received a copy of the GNU General Public License version

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package java.util;

/**

 * A {@link NavigableSet} implementation based on a {@link TreeMap}.

 * The elements are ordered using their {@linkplain Comparable natural

 * ordering}, or by a {@link Comparator} provided at set creation

 * time, depending on which constructor is used.

 *

 * <p>This implementation provides guaranteed log(n) time cost for the basic

 * operations ({@code add}, {@code remove} and {@code contains}).

 *

 * <p>Note that the ordering maintained by a set (whether or not an explicit

 * comparator is provided) must be <i>consistent with equals</i> if it is to

 * correctly implement the {@code Set} interface.  (See {@code Comparable}

 * or {@code Comparator} for a precise definition of <i>consistent with

 * equals</i>.)  This is so because the {@code Set} interface is defined in

 * terms of the {@code equals} operation, but a {@code TreeSet} instance

 * performs all element comparisons using its {@code compareTo} (or

 * {@code compare}) method, so two elements that are deemed equal by this method

 * are, from the standpoint of the set, equal.  The behavior of a set

 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it

 * just fails to obey the general contract of the {@code Set} interface.

 *

 * <p><strong>Note that this implementation is not synchronized.</strong>

 * If multiple threads access a tree set concurrently, and at least one

 * of the threads modifies the set, it <i>must</i> be synchronized

 * externally.  This is typically accomplished by synchronizing on some

 * object that naturally encapsulates the set.

 * If no such object exists, the set should be "wrapped" using the

 * {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}

 * method.  This is best done at creation time, to prevent accidental

 * unsynchronized access to the set: <pre>

 *   SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>

 *

 * <p>The iterators returned by this class's {@code iterator} method are

 * <i>fail-fast</i>: if the set 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 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 is a member of the

 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">

 * Java Collections Framework</a>.

 *

 * @param <E> the type of elements maintained by this set

 *

 * @author  Josh Bloch

 * @see     Collection

 * @see     Set

 * @see     HashSet

 * @see     Comparable

 * @see     Comparator

 * @see     TreeMap

 * @since   1.2

 */

public class TreeSet<E> extends AbstractSet<E>

    implements NavigableSet<E>, Cloneable, java.io.Serializable

{

    /**

     * The backing map.

     */

    private transient NavigableMap<E,Object> m;

    // Dummy value to associate with an Object in the backing Map

    private static final Object PRESENT = new Object();

    /**

     * Constructs a set backed by the specified navigable map.

     */

    TreeSet(NavigableMap<E,Object> m) {

        this.m = m;

    }

    /**

     * Constructs a new, empty tree set, sorted according to the

     * natural ordering of its elements.  All elements inserted into

     * the set must implement the {@link Comparable} interface.

     * Furthermore, all such elements must be <i>mutually

     * comparable</i>: {@code e1.compareTo(e2)} must not throw a

     * {@code ClassCastException} for any elements {@code e1} and

     * {@code e2} in the set.  If the user attempts to add an element

     * to the set that violates this constraint (for example, the user

     * attempts to add a string element to a set whose elements are

     * integers), the {@code add} call will throw a

     * {@code ClassCastException}.

     */

    public TreeSet() {

        this(new TreeMap<>());

    }

    /**

     * Constructs a new, empty tree set, sorted according to the specified

     * comparator.  All elements inserted into the set must be <i>mutually

     * comparable</i> by the specified comparator: {@code comparator.compare(e1,

     * e2)} must not throw a {@code ClassCastException} for any elements

     * {@code e1} and {@code e2} in the set.  If the user attempts to add

     * an element to the set that violates this constraint, the

     * {@code add} call will throw a {@code ClassCastException}.

     *

     * @param comparator the comparator that will be used to order this set.

     *        If {@code null}, the {@linkplain Comparable natural

     *        ordering} of the elements will be used.

     */

    public TreeSet(Comparator<? super E> comparator) {

        this(new TreeMap<>(comparator));

    }

    /**

     * Constructs a new tree set containing the elements in the specified

     * collection, sorted according to the <i>natural ordering</i> of its

     * elements.  All elements inserted into the set must implement the

     * {@link Comparable} interface.  Furthermore, all such elements must be

     * <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a

     * {@code ClassCastException} for any elements {@code e1} and

     * {@code e2} in the set.

     *

     * @param c collection whose elements will comprise the new set

     * @throws ClassCastException if the elements in {@code c} are

     *         not {@link Comparable}, or are not mutually comparable

     * @throws NullPointerException if the specified collection is null

     */

    public TreeSet(Collection<? extends E> c) {

        this();

        addAll(c);

    }

    /**

     * Constructs a new tree set containing the same elements and

     * using the same ordering as the specified sorted set.

     *

     * @param s sorted set whose elements will comprise the new set

     * @throws NullPointerException if the specified sorted set is null

     */

    public TreeSet(SortedSet<E> s) {

        this(s.comparator());

        addAll(s);

    }

    /**

     * Returns an iterator over the elements in this set in ascending order.

     *

     * @return an iterator over the elements in this set in ascending order

     */

    public Iterator<E> iterator() {

        return m.navigableKeySet().iterator();

    }

    /**

     * Returns an iterator over the elements in this set in descending order.

     *

     * @return an iterator over the elements in this set in descending order

     * @since 1.6

     */

    public Iterator<E> descendingIterator() {

        return m.descendingKeySet().iterator();

    }

    /**

     * @since 1.6

     */

    public NavigableSet<E> descendingSet() {

        return new TreeSet<>(m.descendingMap());

    }

    /**

     * Returns the number of elements in this set (its cardinality).

     *

     * @return the number of elements in this set (its cardinality)

     */

    public int size() {

        return m.size();

    }

    /**

     * Returns {@code true} if this set contains no elements.

     *

     * @return {@code true} if this set contains no elements

     */

    public boolean isEmpty() {

        return m.isEmpty();

    }

    /**

     * Returns {@code true} if this set contains the specified element.

     * More formally, returns {@code true} if and only if this set

     * contains an element {@code e} such that

     * {@code Objects.equals(o, e)}.

     *

     * @param o object to be checked for containment in this set

     * @return {@code true} if this set contains the specified element

     * @throws ClassCastException if the specified object cannot be compared

     *         with the elements currently in the set

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     */

    public boolean contains(Object o) {

        return m.containsKey(o);

    }

    /**

     * Adds the specified element to this set if it is not already present.

     * More formally, adds the specified element {@code e} to this set if

     * the set contains no element {@code e2} such that

     * {@code Objects.equals(e, e2)}.

     * If this set already contains the element, the call leaves the set

     * unchanged and returns {@code false}.

     *

     * @param e element to be added to this set

     * @return {@code true} if this set did not already contain the specified

     *         element

     * @throws ClassCastException if the specified object cannot be compared

     *         with the elements currently in this set

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     */

    public boolean add(E e) {

        return m.put(e, PRESENT)==null;

    }

    /**

     * Removes the specified element from this set if it is present.

     * More formally, removes an element {@code e} such that

     * {@code Objects.equals(o, e)},

     * if this set contains such an element.  Returns {@code true} if

     * this set contained the element (or equivalently, if this set

     * changed as a result of the call).  (This set will not contain the

     * element once the call returns.)

     *

     * @param o object to be removed from this set, if present

     * @return {@code true} if this set contained the specified element

     * @throws ClassCastException if the specified object cannot be compared

     *         with the elements currently in this set

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     */

    public boolean remove(Object o) {

        return m.remove(o)==PRESENT;

    }

    /**

     * Removes all of the elements from this set.

     * The set will be empty after this call returns.

     */

    public void clear() {

        m.clear();

    }

    /**

     * Adds all of the elements in the specified collection to this set.

     *

     * @param c collection containing elements to be added to this set

     * @return {@code true} if this set changed as a result of the call

     * @throws ClassCastException if the elements provided cannot be compared

     *         with the elements currently in the set

     * @throws NullPointerException if the specified collection is null or

     *         if any element is null and this set uses natural ordering, or

     *         its comparator does not permit null elements

     */

    public  boolean addAll(Collection<? extends E> c) {

        // Use linear-time version if applicable

        if (m.size()==0 && c.size() > 0 &&

            c instanceof SortedSet &&

            m instanceof TreeMap) {

            SortedSet<? extends E> set = (SortedSet<? extends E>) c;

            TreeMap<E,Object> map = (TreeMap<E, Object>) m;

            if (Objects.equals(set.comparator(), map.comparator())) {

                map.addAllForTreeSet(set, PRESENT);

                return true;

            }

        }

        return super.addAll(c);

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if {@code fromElement} or {@code toElement}

     *         is null and this set uses natural ordering, or its comparator

     *         does not permit null elements

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.6

     */

    public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,

                                  E toElement,   boolean toInclusive) {

        return new TreeSet<>(m.subMap(fromElement, fromInclusive,

                                       toElement,   toInclusive));

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if {@code toElement} is null and

     *         this set uses natural ordering, or its comparator does

     *         not permit null elements

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.6

     */

    public NavigableSet<E> headSet(E toElement, boolean inclusive) {

        return new TreeSet<>(m.headMap(toElement, inclusive));

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if {@code fromElement} is null and

     *         this set uses natural ordering, or its comparator does

     *         not permit null elements

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.6

     */

    public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {

        return new TreeSet<>(m.tailMap(fromElement, inclusive));

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if {@code fromElement} or

     *         {@code toElement} is null and this set uses natural ordering,

     *         or its comparator does not permit null elements

     * @throws IllegalArgumentException {@inheritDoc}

     */

    public SortedSet<E> subSet(E fromElement, E toElement) {

        return subSet(fromElement, true, toElement, false);

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if {@code toElement} is null

     *         and this set uses natural ordering, or its comparator does

     *         not permit null elements

     * @throws IllegalArgumentException {@inheritDoc}

     */

    public SortedSet<E> headSet(E toElement) {

        return headSet(toElement, false);

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if {@code fromElement} is null

     *         and this set uses natural ordering, or its comparator does

     *         not permit null elements

     * @throws IllegalArgumentException {@inheritDoc}

     */

    public SortedSet<E> tailSet(E fromElement) {

        return tailSet(fromElement, true);

    }

    public Comparator<? super E> comparator() {

        return m.comparator();

    }

    /**

     * @throws NoSuchElementException {@inheritDoc}

     */

    public E first() {

        return m.firstKey();

    }

    /**

     * @throws NoSuchElementException {@inheritDoc}

     */

    public E last() {

        return m.lastKey();

    }

    // NavigableSet API methods

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     * @since 1.6

     */

    public E lower(E e) {

        return m.lowerKey(e);

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     * @since 1.6

     */

    public E floor(E e) {

        return m.floorKey(e);

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     * @since 1.6

     */

    public E ceiling(E e) {

        return m.ceilingKey(e);

    }

    /**

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException if the specified element is null

     *         and this set uses natural ordering, or its comparator

     *         does not permit null elements

     * @since 1.6

     */

    public E higher(E e) {

        return m.higherKey(e);

    }

    /**

     * @since 1.6

     */

    public E pollFirst() {

        Map.Entry<E,?> e = m.pollFirstEntry();

        return (e == null) ? null : e.getKey();

    }

    /**

     * @since 1.6

     */

    public E pollLast() {

        Map.Entry<E,?> e = m.pollLastEntry();

        return (e == null) ? null : e.getKey();

    }

    /**

     * Returns a shallow copy of this {@code TreeSet} instance. (The elements

     * themselves are not cloned.)

     *

     * @return a shallow copy of this set

     */

    @SuppressWarnings("unchecked")

    public Object clone() {

        TreeSet<E> clone;

        try {

            clone = (TreeSet<E>) super.clone();

        } catch (CloneNotSupportedException e) {

            throw new InternalError(e);

        }

        clone.m = new TreeMap<>(m);

        return clone;

    }

    /**

     * Save the state of the {@code TreeSet} instance to a stream (that is,

     * serialize it).

     *

     * @serialData Emits the comparator used to order this set, or

     *             {@code null} if it obeys its elements' natural ordering

     *             (Object), followed by the size of the set (the number of

     *             elements it contains) (int), followed by all of its

     *             elements (each an Object) in order (as determined by the

     *             set's Comparator, or by the elements' natural ordering if

     *             the set has no Comparator).

     */

    @java.io.Serial

    private void writeObject(java.io.ObjectOutputStream s)

        throws java.io.IOException {

        // Write out any hidden stuff

        s.defaultWriteObject();

        // Write out Comparator

        s.writeObject(m.comparator());

        // Write out size

        s.writeInt(m.size());

        // Write out all elements in the proper order.

        for (E e : m.keySet())

            s.writeObject(e);

    }

    /**

     * Reconstitute the {@code TreeSet} instance from a stream (that is,

     * deserialize it).

     */

    @java.io.Serial

    private void readObject(java.io.ObjectInputStream s)

        throws java.io.IOException, ClassNotFoundException {

        // Read in any hidden stuff

        s.defaultReadObject();

        // Read in Comparator

        @SuppressWarnings("unchecked")