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	/*
	* Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
	* 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.
	*/

	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<E, Object> map) {
	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
	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")
	Comparator<? super E> c = (Comparator<? super E>) s.readObject();

	// Create backing TreeMap
	TreeMap<E,Object> tm = new TreeMap<>(c);
	m = tm;

	// Read in size
	int size = s.readInt();

	tm.readTreeSet(size, s, PRESENT);
	}

	/**
	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
	* set.
	*
	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
	* {@link Spliterator#DISTINCT}, {@link Spliterator#SORTED}, and
	* {@link Spliterator#ORDERED}. Overriding implementations should document
	* the reporting of additional characteristic values.
	*
	* <p>The spliterator's comparator (see
	* {@link java.util.Spliterator#getComparator()}) is {@code null} if
	* the tree set's comparator (see {@link #comparator()}) is {@code null}.
	* Otherwise, the spliterator's comparator is the same as or imposes the
	* same total ordering as the tree set's comparator.
	*
	* @return a {@code Spliterator} over the elements in this set
	* @since 1.8
	*/
	public Spliterator<E> spliterator() {
	return TreeMap.keySpliteratorFor(m);
	}

	@java.io.Serial
	private static final long serialVersionUID = -2479143000061671589L;
	}

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