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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.Collections2.FilteredCollection;
import com.google.common.math.IntMath;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.NavigableSet;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.function.Consumer;
import java.util.stream.Collector;
import java.util.stream.Stream;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Static utility methods pertaining to {@link Set} instances. Also see this class's counterparts
 * {@link Lists}, {@link Maps} and {@link Queues}.
 *
 * See the Guava User Guide article on  {@code Sets}.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 * @author Chris Povirk
 * @since 2.0
 */
@GwtCompatible(emulated = true)
public final class Sets {
  private Sets() {}

  /**
   * {@link AbstractSet} substitute without the potentially-quadratic {@code removeAll}
   * implementation.
   */
  abstract static class ImprovedAbstractSet extends AbstractSet {
    @Override
    public boolean removeAll(Collection c) {
      return removeAllImpl(this, c);
    }

    @Override
    public boolean retainAll(Collection c) {
      return super.retainAll(checkNotNull(c)); // GWT compatibility
    }
  }

  /**
   * Returns an immutable set instance containing the given enum elements. Internally, the returned
   * set will be backed by an {@link EnumSet}.
   *
   * 
The iteration order of the returned set follows the enum's iteration order, not the order in
   * which the elements are provided to the method.
   *
   * @param anElement one of the elements the set should contain
   * @param otherElements the rest of the elements the set should contain
   * @return an immutable set containing those elements, minus duplicates
   */
  // http://code.google.com/p/google-web-toolkit/issues/detail?id=3028
  @GwtCompatible(serializable = true)
  public static > ImmutableSet immutableEnumSet(
      E anElement, E... otherElements) {
    return ImmutableEnumSet.asImmutable(EnumSet.of(anElement, otherElements));
  }

  /**
   * Returns an immutable set instance containing the given enum elements. Internally, the returned
   * set will be backed by an {@link EnumSet}.
   *
   * 
The iteration order of the returned set follows the enum's iteration order, not the order in
   * which the elements appear in the given collection.
   *
   * @param elements the elements, all of the same {@code enum} type, that the set should contain
   * @return an immutable set containing those elements, minus duplicates
   */
  // http://code.google.com/p/google-web-toolkit/issues/detail?id=3028
  @GwtCompatible(serializable = true)
  public static > ImmutableSet immutableEnumSet(Iterable elements) {
    if (elements instanceof ImmutableEnumSet) {
      return (ImmutableEnumSet) elements;
    } else if (elements instanceof Collection) {
      Collection collection = (Collection) elements;
      if (collection.isEmpty()) {
        return ImmutableSet.of();
      } else {
        return ImmutableEnumSet.asImmutable(EnumSet.copyOf(collection));
      }
    } else {
      Iterator itr = elements.iterator();
      if (itr.hasNext()) {
        EnumSet enumSet = EnumSet.of(itr.next());
        Iterators.addAll(enumSet, itr);
        return ImmutableEnumSet.asImmutable(enumSet);
      } else {
        return ImmutableSet.of();
      }
    }
  }

  private static final class Accumulator> {
    static final Collector, ?, ImmutableSet>> TO_IMMUTABLE_ENUM_SET =
        (Collector)
            Collector.>of(
                Accumulator::new,
                Accumulator::add,
                Accumulator::combine,
                Accumulator::toImmutableSet,
                Collector.Characteristics.UNORDERED);

    @MonotonicNonNull private EnumSet set;

    void add(E e) {
      if (set == null) {
        set = EnumSet.of(e);
      } else {
        set.add(e);
      }
    }

    Accumulator combine(Accumulator other) {
      if (this.set == null) {
        return other;
      } else if (other.set == null) {
        return this;
      } else {
        this.set.addAll(other.set);
        return this;
      }
    }

    ImmutableSet toImmutableSet() {
      return (set == null) ? ImmutableSet.of() : ImmutableEnumSet.asImmutable(set);
    }
  }

  /**
   * Returns a {@code Collector} that accumulates the input elements into a new {@code ImmutableSet}
   * with an implementation specialized for enums. Unlike {@link ImmutableSet#toImmutableSet}, the
   * resulting set will iterate over elements in their enum definition order, not encounter order.
   *
   * @since 21.0
   */
  public static > Collector> toImmutableEnumSet() {
    return (Collector) Accumulator.TO_IMMUTABLE_ENUM_SET;
  }

  /**
   * Returns a new, mutable {@code EnumSet} instance containing the given elements in their
   * natural order. This method behaves identically to {@link EnumSet#copyOf(Collection)}, but also
   * accepts non-{@code Collection} iterables and empty iterables.
   */
  public static > EnumSet newEnumSet(
      Iterable iterable, Class elementType) {
    EnumSet set = EnumSet.noneOf(elementType);
    Iterables.addAll(set, iterable);
    return set;
  }

  // HashSet

  /**
   * Creates a mutable, initially empty {@code HashSet} instance.
   *
   * 
Note: if mutability is not required, use {@link ImmutableSet#of()} instead. If {@code
   * E} is an {@link Enum} type, use {@link EnumSet#noneOf} instead. Otherwise, strongly consider
   * using a {@code LinkedHashSet} instead, at the cost of increased memory footprint, to get
   * deterministic iteration behavior.
   *
   * 
Note for Java 7 and later: this method is now unnecessary and should be treated as
   * deprecated. Instead, use the {@code HashSet} constructor directly, taking advantage of the new
   * "diamond" syntax.
   */
  public static  HashSet newHashSet() {
    return new HashSet();
  }

  /**
   * Creates a mutable {@code HashSet} instance initially containing the given elements.
   *
   * 
Note: if elements are non-null and won't be added or removed after this point, use
   * {@link ImmutableSet#of()} or {@link ImmutableSet#copyOf(Object[])} instead. If {@code E} is an
   * {@link Enum} type, use {@link EnumSet#of(Enum, Enum[])} instead. Otherwise, strongly consider
   * using a {@code LinkedHashSet} instead, at the cost of increased memory footprint, to get
   * deterministic iteration behavior.
   *
   * 
This method is just a small convenience, either for {@code newHashSet(}{@link Arrays#asList
   * asList}{@code (...))}, or for creating an empty set then calling {@link Collections#addAll}.
   * This method is not actually very useful and will likely be deprecated in the future.
   */
  public static  HashSet newHashSet(E... elements) {
    HashSet set = newHashSetWithExpectedSize(elements.length);
    Collections.addAll(set, elements);
    return set;
  }

  /**
   * Creates a mutable {@code HashSet} instance containing the given elements. A very thin
   * convenience for creating an empty set then calling {@link Collection#addAll} or {@link
   * Iterables#addAll}.
   *
   * 
Note: if mutability is not required and the elements are non-null, use {@link
   * ImmutableSet#copyOf(Iterable)} instead. (Or, change {@code elements} to be a {@link
   * FluentIterable} and call {@code elements.toSet()}.)
   *
   * 
Note: if {@code E} is an {@link Enum} type, use {@link #newEnumSet(Iterable, Class)}
   * instead.
   *
   * 
Note for Java 7 and later: if {@code elements} is a {@link Collection}, you don't
   * need this method. Instead, use the {@code HashSet} constructor directly, taking advantage of
   * the new "diamond" syntax.
   *
   * 
Overall, this method is not very useful and will likely be deprecated in the future.
   */
  public static  HashSet newHashSet(Iterable elements) {
    return (elements instanceof Collection)
        ? new HashSet(Collections2.cast(elements))
        : newHashSet(elements.iterator());
  }

  /**
   * Creates a mutable {@code HashSet} instance containing the given elements. A very thin
   * convenience for creating an empty set and then calling {@link Iterators#addAll}.
   *
   * 
Note: if mutability is not required and the elements are non-null, use {@link
   * ImmutableSet#copyOf(Iterator)} instead.
   *
   * 
Note: if {@code E} is an {@link Enum} type, you should create an {@link EnumSet}
   * instead.
   *
   * 
Overall, this method is not very useful and will likely be deprecated in the future.
   */
  public static  HashSet newHashSet(Iterator elements) {
    HashSet set = newHashSet();
    Iterators.addAll(set, elements);
    return set;
  }

  /**
   * Returns a new hash set using the smallest initial table size that can hold {@code expectedSize}
   * elements without resizing. Note that this is not what {@link HashSet#HashSet(int)} does, but it
   * is what most users want and expect it to do.
   *
   * 
This behavior can't be broadly guaranteed, but has been tested with OpenJDK 1.7 and 1.8.
   *
   * @param expectedSize the number of elements you expect to add to the returned set
   * @return a new, empty hash set with enough capacity to hold {@code expectedSize} elements
   *     without resizing
   * @throws IllegalArgumentException if {@code expectedSize} is negative
   */
  public static  HashSet newHashSetWithExpectedSize(int expectedSize) {
    return new HashSet(Maps.capacity(expectedSize));
  }

  /**
   * Creates a thread-safe set backed by a hash map. The set is backed by a {@link
   * ConcurrentHashMap} instance, and thus carries the same concurrency guarantees.
   *
   * 
Unlike {@code HashSet}, this class does NOT allow {@code null} to be used as an element. The
   * set is serializable.
   *
   * @return a new, empty thread-safe {@code Set}
   * @since 15.0
   */
  public static  Set newConcurrentHashSet() {
    return Collections.newSetFromMap(new ConcurrentHashMap());
  }

  /**
   * Creates a thread-safe set backed by a hash map and containing the given elements. The set is
   * backed by a {@link ConcurrentHashMap} instance, and thus carries the same concurrency
   * guarantees.
   *
   * 
Unlike {@code HashSet}, this class does NOT allow {@code null} to be used as an element. The
   * set is serializable.
   *
   * @param elements the elements that the set should contain
   * @return a new thread-safe set containing those elements (minus duplicates)
   * @throws NullPointerException if {@code elements} or any of its contents is null
   * @since 15.0
   */
  public static  Set newConcurrentHashSet(Iterable elements) {
    Set set = newConcurrentHashSet();
    Iterables.addAll(set, elements);
    return set;
  }

  // LinkedHashSet

  /**
   * Creates a mutable, empty {@code LinkedHashSet} instance.
   *
   * 
Note: if mutability is not required, use {@link ImmutableSet#of()} instead.
   *
   * 
Note for Java 7 and later: this method is now unnecessary and should be treated as
   * deprecated. Instead, use the {@code LinkedHashSet} constructor directly, taking advantage of
   * the new "diamond" syntax.
   *
   * @return a new, empty {@code LinkedHashSet}
   */
  public static  LinkedHashSet newLinkedHashSet() {
    return new LinkedHashSet();
  }

  /**
   * Creates a mutable {@code LinkedHashSet} instance containing the given elements in order.
   *
   * 
Note: if mutability is not required and the elements are non-null, use {@link
   * ImmutableSet#copyOf(Iterable)} instead.
   *
   * 
Note for Java 7 and later: if {@code elements} is a {@link Collection}, you don't
   * need this method. Instead, use the {@code LinkedHashSet} constructor directly, taking advantage
   * of the new "diamond" syntax.
   *
   * 
Overall, this method is not very useful and will likely be deprecated in the future.
   *
   * @param elements the elements that the set should contain, in order
   * @return a new {@code LinkedHashSet} containing those elements (minus duplicates)
   */
  public static  LinkedHashSet newLinkedHashSet(Iterable elements) {
    if (elements instanceof Collection) {
      return new LinkedHashSet(Collections2.cast(elements));
    }
    LinkedHashSet set = newLinkedHashSet();
    Iterables.addAll(set, elements);
    return set;
  }

  /**
   * Creates a {@code LinkedHashSet} instance, with a high enough "initial capacity" that it
   * should hold {@code expectedSize} elements without growth. This behavior cannot be
   * broadly guaranteed, but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed
   * that the method isn't inadvertently oversizing the returned set.
   *
   * @param expectedSize the number of elements you expect to add to the returned set
   * @return a new, empty {@code LinkedHashSet} with enough capacity to hold {@code expectedSize}
   *     elements without resizing
   * @throws IllegalArgumentException if {@code expectedSize} is negative
   * @since 11.0
   */
  public static  LinkedHashSet newLinkedHashSetWithExpectedSize(int expectedSize) {
    return new LinkedHashSet(Maps.capacity(expectedSize));
  }

  // TreeSet

  /**
   * Creates a mutable, empty {@code TreeSet} instance sorted by the natural sort ordering of
   * its elements.
   *
   * 
Note: if mutability is not required, use {@link ImmutableSortedSet#of()} instead.
   *
   * 
Note for Java 7 and later: this method is now unnecessary and should be treated as
   * deprecated. Instead, use the {@code TreeSet} constructor directly, taking advantage of the new
   * "diamond" syntax.
   *
   * @return a new, empty {@code TreeSet}
   */
  public static  TreeSet newTreeSet() {
    return new TreeSet();
  }

  /**
   * Creates a mutable {@code TreeSet} instance containing the given elements sorted by their
   * natural ordering.
   *
   * 
Note: if mutability is not required, use {@link ImmutableSortedSet#copyOf(Iterable)}
   * instead.
   *
   * 
Note: If {@code elements} is a {@code SortedSet} with an explicit comparator, this
   * method has different behavior than {@link TreeSet#TreeSet(SortedSet)}, which returns a {@code
   * TreeSet} with that comparator.
   *
   * 
Note for Java 7 and later: this method is now unnecessary and should be treated as
   * deprecated. Instead, use the {@code TreeSet} constructor directly, taking advantage of the new
   * "diamond" syntax.
   *
   * 
This method is just a small convenience for creating an empty set and then calling {@link
   * Iterables#addAll}. This method is not very useful and will likely be deprecated in the future.
   *
   * @param elements the elements that the set should contain
   * @return a new {@code TreeSet} containing those elements (minus duplicates)
   */
  public static  TreeSet newTreeSet(Iterable elements) {
    TreeSet set = newTreeSet();
    Iterables.addAll(set, elements);
    return set;
  }

  /**
   * Creates a mutable, empty {@code TreeSet} instance with the given comparator.
   *
   * 
Note: if mutability is not required, use {@code
   * ImmutableSortedSet.orderedBy(comparator).build()} instead.
   *
   * 
Note for Java 7 and later: this method is now unnecessary and should be treated as
   * deprecated. Instead, use the {@code TreeSet} constructor directly, taking advantage of the new
   * "diamond" syntax. One caveat to this is that the {@code
   * TreeSet} constructor uses a null {@code Comparator} to mean "natural ordering," whereas this
   * factory rejects null. Clean your code accordingly.
   *
   * @param comparator the comparator to use to sort the set
   * @return a new, empty {@code TreeSet}
   * @throws NullPointerException if {@code comparator} is null
   */
  public static  TreeSet newTreeSet(Comparator comparator) {
    return new TreeSet(checkNotNull(comparator));
  }

  /**
   * Creates an empty {@code Set} that uses identity to determine equality. It compares object
   * references, instead of calling {@code equals}, to determine whether a provided object matches
   * an element in the set. For example, {@code contains} returns {@code false} when passed an
   * object that equals a set member, but isn't the same instance. This behavior is similar to the
   * way {@code IdentityHashMap} handles key lookups.
   *
   * @since 8.0
   */
  public static  Set newIdentityHashSet() {
    return Collections.newSetFromMap(Maps.newIdentityHashMap());
  }

  /**
   * Creates an empty {@code CopyOnWriteArraySet} instance.
   *
   * 
Note: if you need an immutable empty {@link Set}, use {@link Collections#emptySet}
   * instead.
   *
   * @return a new, empty {@code CopyOnWriteArraySet}
   * @since 12.0
   */
  @GwtIncompatible // CopyOnWriteArraySet
  public static  CopyOnWriteArraySet newCopyOnWriteArraySet() {
    return new CopyOnWriteArraySet();
  }

  /**
   * Creates a {@code CopyOnWriteArraySet} instance containing the given elements.
   *
   * @param elements the elements that the set should contain, in order
   * @return a new {@code CopyOnWriteArraySet} containing those elements
   * @since 12.0
   */
  @GwtIncompatible // CopyOnWriteArraySet
  public static  CopyOnWriteArraySet newCopyOnWriteArraySet(Iterable elements) {
    // We copy elements to an ArrayList first, rather than incurring the
    // quadratic cost of adding them to the COWAS directly.
    Collection elementsCollection =
        (elements instanceof Collection)
            ? Collections2.cast(elements)
            : Lists.newArrayList(elements);
    return new CopyOnWriteArraySet(elementsCollection);
  }

  /**
   * Creates an {@code EnumSet} consisting of all enum values that are not in the specified
   * collection. If the collection is an {@link EnumSet}, this method has the same behavior as
   * {@link EnumSet#complementOf}. Otherwise, the specified collection must contain at least one
   * element, in order to determine the element type. If the collection could be empty, use {@link
   * #complementOf(Collection, Class)} instead of this method.
   *
   * @param collection the collection whose complement should be stored in the enum set
   * @return a new, modifiable {@code EnumSet} containing all values of the enum that aren't present
   *     in the given collection
   * @throws IllegalArgumentException if {@code collection} is not an {@code EnumSet} instance and
   *     contains no elements
   */
  public static > EnumSet complementOf(Collection collection) {
    if (collection instanceof EnumSet) {
      return EnumSet.complementOf((EnumSet) collection);
    }
    checkArgument(
        !collection.isEmpty(), "collection is empty; use the other version of this method");
    Class type = collection.iterator().next().getDeclaringClass();
    return makeComplementByHand(collection, type);
  }

  /**
   * Creates an {@code EnumSet} consisting of all enum values that are not in the specified
   * collection. This is equivalent to {@link EnumSet#complementOf}, but can act on any input
   * collection, as long as the elements are of enum type.
   *
   * @param collection the collection whose complement should be stored in the {@code EnumSet}
   * @param type the type of the elements in the set
   * @return a new, modifiable {@code EnumSet} initially containing all the values of the enum not
   *     present in the given collection
   */
  public static > EnumSet complementOf(
      Collection collection, Class type) {
    checkNotNull(collection);
    return (collection instanceof EnumSet)
        ? EnumSet.complementOf((EnumSet) collection)
        : makeComplementByHand(collection, type);
  }

  private static > EnumSet makeComplementByHand(
      Collection collection, Class type) {
    EnumSet result = EnumSet.allOf(type);
    result.removeAll(collection);
    return result;
  }

  /**
   * Returns a set backed by the specified map. The resulting set displays the same ordering,
   * concurrency, and performance characteristics as the backing map. In essence, this factory
   * method provides a {@link Set} implementation corresponding to any {@link Map} implementation.
   * There is no need to use this method on a {@link Map} implementation that already has a
   * corresponding {@link Set} implementation (such as {@link java.util.HashMap} or {@link
   * java.util.TreeMap}).
   *
   * 
Each method invocation on the set returned by this method results in exactly one method
   * invocation on the backing map or its {@code keySet} view, with one exception. The {@code
   * addAll} method is implemented as a sequence of {@code put} invocations on the backing map.
   *
   * 
The specified map must be empty at the time this method is invoked, and should not be
   * accessed directly after this method returns. These conditions are ensured if the map is created
   * empty, passed directly to this method, and no reference to the map is retained, as illustrated
   * in the following code fragment:
   *
   * 
{@code
   * Set