/*
    * 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.checkState;
  import static com.google.common.collect.CollectPreconditions.checkNonnegative;
  import static com.google.common.collect.CollectPreconditions.checkRemove;
  
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.annotations.GwtIncompatible;
  import com.google.common.base.MoreObjects;
  import com.google.common.primitives.Ints;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.io.Serializable;
  import java.util.Comparator;
  import java.util.ConcurrentModificationException;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import javax.annotation.Nullable;
  
  /**
   * A multiset which maintains the ordering of its elements, according to either their natural order
   * or an explicit {@link Comparator}. In all cases, this implementation uses
   * {@link Comparable#compareTo} or {@link Comparator#compare} instead of {@link Object#equals} to
   * determine equivalence of instances.
   *
   * <p><b>Warning:</b> The comparison must be <i>consistent with equals</i> as explained by the
   * {@link Comparable} class specification. Otherwise, the resulting multiset will violate the
   * {@link java.util.Collection} contract, which is specified in terms of {@link Object#equals}.
   *
   * <p>See the Guava User Guide article on <a href=
   * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multiset">
   * {@code Multiset}</a>.
   *
   * @author Louis Wasserman
   * @author Jared Levy
   * @since 2.0 (imported from Google Collections Library)
   */
  @GwtCompatible(emulated = true)
  public final class TreeMultiset<E> extends AbstractSortedMultiset<E> implements Serializable {
  
    /**
     * Creates a new, empty multiset, sorted according to the elements' natural order. All elements
     * inserted into the multiset must implement the {@code 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 multiset. If the
     * user attempts to add an element to the multiset that violates this constraint (for example,
     * the user attempts to add a string element to a set whose elements are integers), the
     * {@code add(Object)} call will throw a {@code ClassCastException}.
     *
     * <p>The type specification is {@code <E extends Comparable>}, instead of the more specific
     * {@code <E extends Comparable<? super E>>}, to support classes defined without generics.
     */
    public static <E extends Comparable> TreeMultiset<E> create() {
      return new TreeMultiset<E>(Ordering.natural());
    }
  
    /**
     * Creates a new, empty multiset, sorted according to the specified comparator. All elements
     * inserted into the multiset 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 multiset. If the user attempts to add an element to the multiset that violates this
     * constraint, the {@code add(Object)} call will throw a {@code ClassCastException}.
     *
     * @param comparator
     *          the comparator that will be used to sort this multiset. A null value indicates that
     *          the elements' <i>natural ordering</i> should be used.
     */
    @SuppressWarnings("unchecked")
    public static <E> TreeMultiset<E> create(@Nullable Comparator<? super E> comparator) {
      return (comparator == null)
          ? new TreeMultiset<E>((Comparator) Ordering.natural())
          : new TreeMultiset<E>(comparator);
    }
  
    /**
     * Creates an empty multiset containing the given initial elements, sorted according to the
     * elements' natural order.
     *
    * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
    *
    * <p>The type specification is {@code <E extends Comparable>}, instead of the more specific
    * {@code <E extends Comparable<? super E>>}, to support classes defined without generics.
    */
   public static <E extends Comparable> TreeMultiset<E> create(Iterable<? extends E> elements) {
     TreeMultiset<E> multiset = create();
     Iterables.addAll(multiset, elements);
     return multiset;
   }
 
   private final transient Reference<AvlNode<E>> rootReference;
   private final transient GeneralRange<E> range;
   private final transient AvlNode<E> header;
 
   TreeMultiset(Reference<AvlNode<E>> rootReference, GeneralRange<E> range, AvlNode<E> endLink) {
     super(range.comparator());
     this.rootReference = rootReference;
     this.range = range;
     this.header = endLink;
   }
 
   TreeMultiset(Comparator<? super E> comparator) {
     super(comparator);
     this.range = GeneralRange.all(comparator);
     this.header = new AvlNode<E>(null, 1);
     successor(header, header);
     this.rootReference = new Reference<AvlNode<E>>();
   }
 
   /**
    * A function which can be summed across a subtree.
    */
   private enum Aggregate {
     SIZE {
       @Override
       int nodeAggregate(AvlNode<?> node) {
         return node.elemCount;
       }
 
       @Override
       long treeAggregate(@Nullable AvlNode<?> root) {
         return (root == null) ? 0 : root.totalCount;
       }
     },
     DISTINCT {
       @Override
       int nodeAggregate(AvlNode<?> node) {
         return 1;
       }
 
       @Override
       long treeAggregate(@Nullable AvlNode<?> root) {
         return (root == null) ? 0 : root.distinctElements;
       }
     };
     abstract int nodeAggregate(AvlNode<?> node);
 
     abstract long treeAggregate(@Nullable AvlNode<?> root);
   }
 
   private long aggregateForEntries(Aggregate aggr) {
     AvlNode<E> root = rootReference.get();
     long total = aggr.treeAggregate(root);
     if (range.hasLowerBound()) {
       total -= aggregateBelowRange(aggr, root);
     }
     if (range.hasUpperBound()) {
       total -= aggregateAboveRange(aggr, root);
     }
     return total;
   }
 
   private long aggregateBelowRange(Aggregate aggr, @Nullable AvlNode<E> node) {
     if (node == null) {
       return 0;
     }
     int cmp = comparator().compare(range.getLowerEndpoint(), node.elem);
     if (cmp < 0) {
       return aggregateBelowRange(aggr, node.left);
     } else if (cmp == 0) {
       switch (range.getLowerBoundType()) {
         case OPEN:
           return aggr.nodeAggregate(node) + aggr.treeAggregate(node.left);
         case CLOSED:
           return aggr.treeAggregate(node.left);
         default:
           throw new AssertionError();
       }
     } else {
       return aggr.treeAggregate(node.left) + aggr.nodeAggregate(node)
           + aggregateBelowRange(aggr, node.right);
     }
   }
 
   private long aggregateAboveRange(Aggregate aggr, @Nullable AvlNode<E> node) {
     if (node == null) {
       return 0;
     }
     int cmp = comparator().compare(range.getUpperEndpoint(), node.elem);
     if (cmp > 0) {
       return aggregateAboveRange(aggr, node.right);
     } else if (cmp == 0) {
       switch (range.getUpperBoundType()) {
         case OPEN:
           return aggr.nodeAggregate(node) + aggr.treeAggregate(node.right);
         case CLOSED:
           return aggr.treeAggregate(node.right);
         default:
           throw new AssertionError();
       }
     } else {
       return aggr.treeAggregate(node.right) + aggr.nodeAggregate(node)
           + aggregateAboveRange(aggr, node.left);
     }
   }
 
   @Override
   public int size() {
     return Ints.saturatedCast(aggregateForEntries(Aggregate.SIZE));
   }
 
   @Override
   int distinctElements() {
     return Ints.saturatedCast(aggregateForEntries(Aggregate.DISTINCT));
   }
 
   @Override
   public int count(@Nullable Object element) {
     try {
       @SuppressWarnings("unchecked")
       E e = (E) element;
       AvlNode<E> root = rootReference.get();
       if (!range.contains(e) || root == null) {
         return 0;
       }
       return root.count(comparator(), e);
     } catch (ClassCastException e) {
       return 0;
     } catch (NullPointerException e) {
       return 0;
     }
   }
 
   @Override
   public int add(@Nullable E element, int occurrences) {
     checkNonnegative(occurrences, "occurrences");
     if (occurrences == 0) {
       return count(element);
     }
     checkArgument(range.contains(element));
     AvlNode<E> root = rootReference.get();
     if (root == null) {
       comparator().compare(element, element);
       AvlNode<E> newRoot = new AvlNode<E>(element, occurrences);
       successor(header, newRoot, header);
       rootReference.checkAndSet(root, newRoot);
       return 0;
     }
     int[] result = new int[1]; // used as a mutable int reference to hold result
     AvlNode<E> newRoot = root.add(comparator(), element, occurrences, result);
     rootReference.checkAndSet(root, newRoot);
     return result[0];
   }
 
   @Override
   public int remove(@Nullable Object element, int occurrences) {
     checkNonnegative(occurrences, "occurrences");
     if (occurrences == 0) {
       return count(element);
     }
     AvlNode<E> root = rootReference.get();
     int[] result = new int[1]; // used as a mutable int reference to hold result
     AvlNode<E> newRoot;
     try {
       @SuppressWarnings("unchecked")
       E e = (E) element;
       if (!range.contains(e) || root == null) {
         return 0;
       }
       newRoot = root.remove(comparator(), e, occurrences, result);
     } catch (ClassCastException e) {
       return 0;
     } catch (NullPointerException e) {
       return 0;
     }
     rootReference.checkAndSet(root, newRoot);
     return result[0];
   }
 
   @Override
   public int setCount(@Nullable E element, int count) {
     checkNonnegative(count, "count");
     if (!range.contains(element)) {
       checkArgument(count == 0);
       return 0;
     }
 
     AvlNode<E> root = rootReference.get();
     if (root == null) {
       if (count > 0) {
         add(element, count);
       }
       return 0;
     }
     int[] result = new int[1]; // used as a mutable int reference to hold result
     AvlNode<E> newRoot = root.setCount(comparator(), element, count, result);
     rootReference.checkAndSet(root, newRoot);
     return result[0];
   }
 
   @Override
   public boolean setCount(@Nullable E element, int oldCount, int newCount) {
     checkNonnegative(newCount, "newCount");
     checkNonnegative(oldCount, "oldCount");
     checkArgument(range.contains(element));
 
     AvlNode<E> root = rootReference.get();
     if (root == null) {
       if (oldCount == 0) {
         if (newCount > 0) {
           add(element, newCount);
         }
         return true;
       } else {
         return false;
       }
     }
     int[] result = new int[1]; // used as a mutable int reference to hold result
     AvlNode<E> newRoot = root.setCount(comparator(), element, oldCount, newCount, result);
     rootReference.checkAndSet(root, newRoot);
     return result[0] == oldCount;
   }
 
   private Entry<E> wrapEntry(final AvlNode<E> baseEntry) {
     return new Multisets.AbstractEntry<E>() {
       @Override
       public E getElement() {
         return baseEntry.getElement();
       }
 
       @Override
       public int getCount() {
         int result = baseEntry.getCount();
         if (result == 0) {
           return count(getElement());
         } else {
           return result;
         }
       }
     };
   }
 
   /**
    * Returns the first node in the tree that is in range.
    */
   @Nullable private AvlNode<E> firstNode() {
     AvlNode<E> root = rootReference.get();
     if (root == null) {
       return null;
     }
     AvlNode<E> node;
     if (range.hasLowerBound()) {
       E endpoint = range.getLowerEndpoint();
       node = rootReference.get().ceiling(comparator(), endpoint);
       if (node == null) {
         return null;
       }
       if (range.getLowerBoundType() == BoundType.OPEN
           && comparator().compare(endpoint, node.getElement()) == 0) {
         node = node.succ;
       }
     } else {
       node = header.succ;
     }
     return (node == header || !range.contains(node.getElement())) ? null : node;
   }
 
   @Nullable private AvlNode<E> lastNode() {
     AvlNode<E> root = rootReference.get();
     if (root == null) {
       return null;
     }
     AvlNode<E> node;
     if (range.hasUpperBound()) {
       E endpoint = range.getUpperEndpoint();
       node = rootReference.get().floor(comparator(), endpoint);
       if (node == null) {
         return null;
       }
       if (range.getUpperBoundType() == BoundType.OPEN
           && comparator().compare(endpoint, node.getElement()) == 0) {
         node = node.pred;
       }
     } else {
       node = header.pred;
     }
     return (node == header || !range.contains(node.getElement())) ? null : node;
   }
 
   @Override
   Iterator<Entry<E>> entryIterator() {
     return new Iterator<Entry<E>>() {
       AvlNode<E> current = firstNode();
       Entry<E> prevEntry;
 
       @Override
       public boolean hasNext() {
         if (current == null) {
           return false;
         } else if (range.tooHigh(current.getElement())) {
           current = null;
           return false;
         } else {
           return true;
         }
       }
 
       @Override
       public Entry<E> next() {
         if (!hasNext()) {
           throw new NoSuchElementException();
         }
         Entry<E> result = wrapEntry(current);
         prevEntry = result;
         if (current.succ == header) {
           current = null;
         } else {
           current = current.succ;
         }
         return result;
       }
 
       @Override
       public void remove() {
         checkRemove(prevEntry != null);
         setCount(prevEntry.getElement(), 0);
         prevEntry = null;
       }
     };
   }
 
   @Override
   Iterator<Entry<E>> descendingEntryIterator() {
     return new Iterator<Entry<E>>() {
       AvlNode<E> current = lastNode();
       Entry<E> prevEntry = null;
 
       @Override
       public boolean hasNext() {
         if (current == null) {
           return false;
         } else if (range.tooLow(current.getElement())) {
           current = null;
           return false;
         } else {
           return true;
         }
       }
 
       @Override
       public Entry<E> next() {
         if (!hasNext()) {
           throw new NoSuchElementException();
         }
         Entry<E> result = wrapEntry(current);
         prevEntry = result;
         if (current.pred == header) {
           current = null;
         } else {
           current = current.pred;
         }
         return result;
       }
 
       @Override
       public void remove() {
         checkRemove(prevEntry != null);
         setCount(prevEntry.getElement(), 0);
         prevEntry = null;
       }
     };
   }
 
   @Override
   public SortedMultiset<E> headMultiset(@Nullable E upperBound, BoundType boundType) {
     return new TreeMultiset<E>(rootReference, range.intersect(GeneralRange.upTo(
         comparator(),
         upperBound,
         boundType)), header);
   }
 
   @Override
   public SortedMultiset<E> tailMultiset(@Nullable E lowerBound, BoundType boundType) {
     return new TreeMultiset<E>(rootReference, range.intersect(GeneralRange.downTo(
         comparator(),
         lowerBound,
         boundType)), header);
   }
 
   static int distinctElements(@Nullable AvlNode<?> node) {
     return (node == null) ? 0 : node.distinctElements;
   }
 
   private static final class Reference<T> {
     @Nullable private T value;
 
     @Nullable public T get() {
       return value;
     }
 
     public void checkAndSet(@Nullable T expected, T newValue) {
       if (value != expected) {
         throw new ConcurrentModificationException();
       }
       value = newValue;
     }
   }
 
   private static final class AvlNode<E> extends Multisets.AbstractEntry<E> {
     @Nullable private final E elem;
 
     // elemCount is 0 iff this node has been deleted.
     private int elemCount;
 
     private int distinctElements;
     private long totalCount;
     private int height;
     private AvlNode<E> left;
     private AvlNode<E> right;
     private AvlNode<E> pred;
     private AvlNode<E> succ;
 
     AvlNode(@Nullable E elem, int elemCount) {
       checkArgument(elemCount > 0);
       this.elem = elem;
       this.elemCount = elemCount;
       this.totalCount = elemCount;
       this.distinctElements = 1;
       this.height = 1;
       this.left = null;
       this.right = null;
     }
 
     public int count(Comparator<? super E> comparator, E e) {
       int cmp = comparator.compare(e, elem);
       if (cmp < 0) {
         return (left == null) ? 0 : left.count(comparator, e);
       } else if (cmp > 0) {
         return (right == null) ? 0 : right.count(comparator, e);
       } else {
         return elemCount;
       }
     }
 
     private AvlNode<E> addRightChild(E e, int count) {
       right = new AvlNode<E>(e, count);
       successor(this, right, succ);
       height = Math.max(2, height);
       distinctElements++;
       totalCount += count;
       return this;
     }
 
     private AvlNode<E> addLeftChild(E e, int count) {
       left = new AvlNode<E>(e, count);
       successor(pred, left, this);
       height = Math.max(2, height);
       distinctElements++;
       totalCount += count;
       return this;
     }
 
     AvlNode<E> add(Comparator<? super E> comparator, @Nullable E e, int count, int[] result) {
       /*
        * It speeds things up considerably to unconditionally add count to totalCount here,
        * but that destroys failure atomicity in the case of count overflow. =(
        */
       int cmp = comparator.compare(e, elem);
       if (cmp < 0) {
         AvlNode<E> initLeft = left;
         if (initLeft == null) {
           result[0] = 0;
           return addLeftChild(e, count);
         }
         int initHeight = initLeft.height;
 
         left = initLeft.add(comparator, e, count, result);
         if (result[0] == 0) {
           distinctElements++;
         }
         this.totalCount += count;
         return (left.height == initHeight) ? this : rebalance();
       } else if (cmp > 0) {
         AvlNode<E> initRight = right;
         if (initRight == null) {
           result[0] = 0;
           return addRightChild(e, count);
         }
         int initHeight = initRight.height;
 
         right = initRight.add(comparator, e, count, result);
         if (result[0] == 0) {
           distinctElements++;
         }
         this.totalCount += count;
         return (right.height == initHeight) ? this : rebalance();
       }
 
       // adding count to me!  No rebalance possible.
       result[0] = elemCount;
       long resultCount = (long) elemCount + count;
       checkArgument(resultCount <= Integer.MAX_VALUE);
       this.elemCount += count;
       this.totalCount += count;
       return this;
     }
 
     AvlNode<E> remove(Comparator<? super E> comparator, @Nullable E e, int count, int[] result) {
       int cmp = comparator.compare(e, elem);
       if (cmp < 0) {
         AvlNode<E> initLeft = left;
         if (initLeft == null) {
           result[0] = 0;
           return this;
         }
 
         left = initLeft.remove(comparator, e, count, result);
 
         if (result[0] > 0) {
           if (count >= result[0]) {
             this.distinctElements--;
             this.totalCount -= result[0];
           } else {
             this.totalCount -= count;
           }
         }
         return (result[0] == 0) ? this : rebalance();
       } else if (cmp > 0) {
         AvlNode<E> initRight = right;
         if (initRight == null) {
           result[0] = 0;
           return this;
         }
 
         right = initRight.remove(comparator, e, count, result);
 
         if (result[0] > 0) {
           if (count >= result[0]) {
             this.distinctElements--;
             this.totalCount -= result[0];
           } else {
             this.totalCount -= count;
           }
         }
         return rebalance();
       }
 
       // removing count from me!
       result[0] = elemCount;
       if (count >= elemCount) {
         return deleteMe();
       } else {
         this.elemCount -= count;
         this.totalCount -= count;
         return this;
       }
     }
 
     AvlNode<E> setCount(Comparator<? super E> comparator, @Nullable E e, int count, int[] result) {
       int cmp = comparator.compare(e, elem);
       if (cmp < 0) {
         AvlNode<E> initLeft = left;
         if (initLeft == null) {
           result[0] = 0;
           return (count > 0) ? addLeftChild(e, count) : this;
         }
 
         left = initLeft.setCount(comparator, e, count, result);
 
         if (count == 0 && result[0] != 0) {
           this.distinctElements--;
         } else if (count > 0 && result[0] == 0) {
           this.distinctElements++;
         }
 
         this.totalCount += count - result[0];
         return rebalance();
       } else if (cmp > 0) {
         AvlNode<E> initRight = right;
         if (initRight == null) {
           result[0] = 0;
           return (count > 0) ? addRightChild(e, count) : this;
         }
 
         right = initRight.setCount(comparator, e, count, result);
 
         if (count == 0 && result[0] != 0) {
           this.distinctElements--;
         } else if (count > 0 && result[0] == 0) {
           this.distinctElements++;
         }
 
         this.totalCount += count - result[0];
         return rebalance();
       }
 
       // setting my count
       result[0] = elemCount;
       if (count == 0) {
         return deleteMe();
       }
       this.totalCount += count - elemCount;
       this.elemCount = count;
       return this;
     }
 
     AvlNode<E> setCount(
         Comparator<? super E> comparator,
         @Nullable E e,
         int expectedCount,
         int newCount,
         int[] result) {
       int cmp = comparator.compare(e, elem);
       if (cmp < 0) {
         AvlNode<E> initLeft = left;
         if (initLeft == null) {
           result[0] = 0;
           if (expectedCount == 0 && newCount > 0) {
             return addLeftChild(e, newCount);
           }
           return this;
         }
 
         left = initLeft.setCount(comparator, e, expectedCount, newCount, result);
 
         if (result[0] == expectedCount) {
           if (newCount == 0 && result[0] != 0) {
             this.distinctElements--;
           } else if (newCount > 0 && result[0] == 0) {
             this.distinctElements++;
           }
           this.totalCount += newCount - result[0];
         }
         return rebalance();
       } else if (cmp > 0) {
         AvlNode<E> initRight = right;
         if (initRight == null) {
           result[0] = 0;
           if (expectedCount == 0 && newCount > 0) {
             return addRightChild(e, newCount);
           }
           return this;
         }
 
         right = initRight.setCount(comparator, e, expectedCount, newCount, result);
 
         if (result[0] == expectedCount) {
           if (newCount == 0 && result[0] != 0) {
             this.distinctElements--;
           } else if (newCount > 0 && result[0] == 0) {
             this.distinctElements++;
           }
           this.totalCount += newCount - result[0];
         }
         return rebalance();
       }
 
       // setting my count
       result[0] = elemCount;
       if (expectedCount == elemCount) {
         if (newCount == 0) {
           return deleteMe();
         }
         this.totalCount += newCount - elemCount;
         this.elemCount = newCount;
       }
       return this;
     }
 
     private AvlNode<E> deleteMe() {
       int oldElemCount = this.elemCount;
       this.elemCount = 0;
       successor(pred, succ);
       if (left == null) {
         return right;
       } else if (right == null) {
         return left;
       } else if (left.height >= right.height) {
         AvlNode<E> newTop = pred;
         // newTop is the maximum node in my left subtree
         newTop.left = left.removeMax(newTop);
         newTop.right = right;
         newTop.distinctElements = distinctElements - 1;
         newTop.totalCount = totalCount - oldElemCount;
         return newTop.rebalance();
       } else {
         AvlNode<E> newTop = succ;
         newTop.right = right.removeMin(newTop);
         newTop.left = left;
         newTop.distinctElements = distinctElements - 1;
         newTop.totalCount = totalCount - oldElemCount;
         return newTop.rebalance();
       }
     }
 
     // Removes the minimum node from this subtree to be reused elsewhere
     private AvlNode<E> removeMin(AvlNode<E> node) {
       if (left == null) {
         return right;
       } else {
         left = left.removeMin(node);
         distinctElements--;
         totalCount -= node.elemCount;
         return rebalance();
       }
     }
 
     // Removes the maximum node from this subtree to be reused elsewhere
     private AvlNode<E> removeMax(AvlNode<E> node) {
       if (right == null) {
         return left;
       } else {
         right = right.removeMax(node);
         distinctElements--;
         totalCount -= node.elemCount;
         return rebalance();
       }
     }
 
     private void recomputeMultiset() {
       this.distinctElements = 1 + TreeMultiset.distinctElements(left)
           + TreeMultiset.distinctElements(right);
       this.totalCount = elemCount + totalCount(left) + totalCount(right);
     }
 
     private void recomputeHeight() {
       this.height = 1 + Math.max(height(left), height(right));
     }
 
     private void recompute() {
       recomputeMultiset();
       recomputeHeight();
     }
 
     private AvlNode<E> rebalance() {
       switch (balanceFactor()) {
         case -2:
           if (right.balanceFactor() > 0) {
             right = right.rotateRight();
           }
           return rotateLeft();
         case 2:
           if (left.balanceFactor() < 0) {
             left = left.rotateLeft();
           }
           return rotateRight();
         default:
           recomputeHeight();
           return this;
       }
     }
 
     private int balanceFactor() {
       return height(left) - height(right);
     }
 
     private AvlNode<E> rotateLeft() {
       checkState(right != null);
       AvlNode<E> newTop = right;
       this.right = newTop.left;
       newTop.left = this;
       newTop.totalCount = this.totalCount;
       newTop.distinctElements = this.distinctElements;
       this.recompute();
       newTop.recomputeHeight();
       return newTop;
     }
 
     private AvlNode<E> rotateRight() {
       checkState(left != null);
       AvlNode<E> newTop = left;
       this.left = newTop.right;
       newTop.right = this;
       newTop.totalCount = this.totalCount;
       newTop.distinctElements = this.distinctElements;
       this.recompute();
       newTop.recomputeHeight();
       return newTop;
     }
 
     private static long totalCount(@Nullable AvlNode<?> node) {
       return (node == null) ? 0 : node.totalCount;
     }
 
     private static int height(@Nullable AvlNode<?> node) {
       return (node == null) ? 0 : node.height;
     }
 
     @Nullable private AvlNode<E> ceiling(Comparator<? super E> comparator, E e) {
       int cmp = comparator.compare(e, elem);
       if (cmp < 0) {
         return (left == null) ? this : MoreObjects.firstNonNull(left.ceiling(comparator, e), this);
       } else if (cmp == 0) {
         return this;
       } else {
         return (right == null) ? null : right.ceiling(comparator, e);
       }
     }
 
     @Nullable private AvlNode<E> floor(Comparator<? super E> comparator, E e) {
       int cmp = comparator.compare(e, elem);
       if (cmp > 0) {
         return (right == null) ? this : MoreObjects.firstNonNull(right.floor(comparator, e), this);
       } else if (cmp == 0) {
         return this;
       } else {
         return (left == null) ? null : left.floor(comparator, e);
       }
     }
 
     @Override
     public E getElement() {
       return elem;
     }
 
     @Override
     public int getCount() {
       return elemCount;
     }
 
     @Override
     public String toString() {
       return Multisets.immutableEntry(getElement(), getCount()).toString();
     }
   }
 
   private static <T> void successor(AvlNode<T> a, AvlNode<T> b) {
     a.succ = b;
     b.pred = a;
   }
 
   private static <T> void successor(AvlNode<T> a, AvlNode<T> b, AvlNode<T> c) {
     successor(a, b);
     successor(b, c);
   }
 
   /*
    * TODO(jlevy): Decide whether entrySet() should return entries with an equals() method that
    * calls the comparator to compare the two keys. If that change is made,
    * AbstractMultiset.equals() can simply check whether two multisets have equal entry sets.
    */
 
   /**
    * @serialData the comparator, the number of distinct elements, the first element, its count, the
    *             second element, its count, and so on
    */
   @GwtIncompatible("java.io.ObjectOutputStream")
   private void writeObject(ObjectOutputStream stream) throws IOException {
     stream.defaultWriteObject();
     stream.writeObject(elementSet().comparator());
     Serialization.writeMultiset(this, stream);
   }
 
   @GwtIncompatible("java.io.ObjectInputStream")
   private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
     stream.defaultReadObject();
     @SuppressWarnings("unchecked")
     // reading data stored by writeObject
     Comparator<? super E> comparator = (Comparator<? super E>) stream.readObject();
     Serialization.getFieldSetter(AbstractSortedMultiset.class, "comparator").set(this, comparator);
     Serialization.getFieldSetter(TreeMultiset.class, "range").set(
         this,
         GeneralRange.all(comparator));
     Serialization.getFieldSetter(TreeMultiset.class, "rootReference").set(
         this,
         new Reference<AvlNode<E>>());
     AvlNode<E> header = new AvlNode<E>(null, 1);
     Serialization.getFieldSetter(TreeMultiset.class, "header").set(this, header);
     successor(header, header);
     Serialization.populateMultiset(this, stream);
   }
 
   @GwtIncompatible("not needed in emulated source") private static final long serialVersionUID = 1;
 }