SplayTree`2.cs

/* ---- MIT LICENSE ----
Copyright (c) 2011 John Gietzen

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
------------------------*/

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;

public class SplayTree<TKey, TValue> : IDictionary<TKey, TValue> where TKey : IComparable<TKey>
{
    private SplayTreeNode root;
    private int count;
    private int version = 0;

    public void Add(TKey key, TValue value)
    {
        this.Set(key, value, throwOnExisting: true);
    }

    public void Add(KeyValuePair<TKey, TValue> item)
    {
        this.Set(item.Key, item.Value, throwOnExisting: true);
    }

    private void Set(TKey key, TValue value, bool throwOnExisting)
    {
        if (this.count == 0)
        {
            this.version++;
            this.root = new SplayTreeNode(key, value);
            this.count = 1;
            return;
        }

        this.Splay(key);

        var c = key.CompareTo(this.root.Key);
        if (c == 0)
        {
            if (throwOnExisting)
            {
                throw new ArgumentException("An item with the same key already exists in the tree.");
            }

            this.version++;
            this.root.Value = value;
            return;
        }

        var n = new SplayTreeNode(key, value);
        if (c < 0)
        {
            n.LeftChild = this.root.LeftChild;
            n.RightChild = this.root;
            this.root.LeftChild = null;
        }
        else
        {
            n.RightChild = this.root.RightChild;
            n.LeftChild = this.root;
            this.root.RightChild = null;
        }

        this.root = n;
        this.count++;
        this.Splay(key);
        this.version++;
    }

    public void Clear()
    {
        this.root = null;
        this.count = 0;
        this.version++;
    }

    public bool ContainsKey(TKey key)
    {
        if (this.count == 0)
        {
            return false;
        }

        this.Splay(key);

        return key.CompareTo(this.root.Key) == 0;
    }

    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
        if (this.count == 0)
        {
            return false;
        }

        this.Splay(item.Key);

        return item.Key.CompareTo(this.root.Key) == 0 && (object.ReferenceEquals(this.root.Value, item.Value) || (!object.ReferenceEquals(item.Value, null) && item.Value.Equals(this.root.Value)));
    }

    private void Splay(TKey key)
    {
        SplayTreeNode l, r, t, y, header;
        l = r = header = new SplayTreeNode(default(TKey), default(TValue));
        t = this.root;
        while (true)
        {
            var c = key.CompareTo(t.Key);
            if (c < 0)
            {
                if (t.LeftChild == null) break;
                if (key.CompareTo(t.LeftChild.Key) < 0)
                {
                    y = t.LeftChild;
                    t.LeftChild = y.RightChild;
                    y.RightChild = t;
                    t = y;
                    if (t.LeftChild == null) break;
                }
                r.LeftChild = t;
                r = t;
                t = t.LeftChild;
            }
            else if (c > 0)
            {
                if (t.RightChild == null) break;
                if (key.CompareTo(t.RightChild.Key) > 0)
                {
                    y = t.RightChild;
                    t.RightChild = y.LeftChild;
                    y.LeftChild = t;
                    t = y;
                    if (t.RightChild == null) break;
                }
                l.RightChild = t;
                l = t;
                t = t.RightChild;
            }
            else
            {
                break;
            }
        }
        l.RightChild = t.LeftChild;
        r.LeftChild = t.RightChild;
        t.LeftChild = header.RightChild;
        t.RightChild = header.LeftChild;
        this.root = t;
    }

    public bool Remove(TKey key)
    {
        if (this.count == 0)
        {
            return false;
        }

        this.Splay(key);

        if (key.CompareTo(this.root.Key) != 0)
        {
            return false;
        }

        if (this.root.LeftChild == null)
        {
            this.root = this.root.RightChild;
        }
        else
        {
            var swap = this.root.RightChild;
            this.root = this.root.LeftChild;
            this.Splay(key);
            this.root.RightChild = swap;
        }

        this.version++;
        this.count--;
        return true;
    }

    public bool TryGetValue(TKey key, out TValue value)
    {
        if (this.count == 0)
        {
            value = default(TValue);
            return false;
        }

        this.Splay(key);
        if (key.CompareTo(this.root.Key) != 0)
        {
            value = default(TValue);
            return false;
        }

        value = this.root.Value;
        return true;
    }

    public TValue this[TKey key]
    {
        get
        {
            if (this.count == 0)
            {
                throw new KeyNotFoundException("The key was not found in the tree.");
            }

            this.Splay(key);
            if (key.CompareTo(this.root.Key) != 0)
            {
                throw new KeyNotFoundException("The key was not found in the tree.");
            }

            return this.root.Value;
        }

        set
        {
            this.Set(key, value, throwOnExisting: false);
        }
    }

    public int Count
    {
        get { return this.count; }
    }

    public bool IsReadOnly
    {
        get { return false; }
    }

    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
        if (this.count == 0)
        {
            return false;
        }

        this.Splay(item.Key);

        if (item.Key.CompareTo(this.root.Key) == 0 && (object.ReferenceEquals(this.root.Value, item.Value) || (!object.ReferenceEquals(item.Value, null) && item.Value.Equals(this.root.Value))))
        {
            return false;
        }

        if (this.root.LeftChild == null)
        {
            this.root = this.root.RightChild;
        }
        else
        {
            var swap = this.root.RightChild;
            this.root = this.root.LeftChild;
            this.Splay(item.Key);
            this.root.RightChild = swap;
        }

        this.version++;
        this.count--;
        return true;
    }

    public void Trim(int depth)
    {
        if (depth < 0)
        {
            throw new ArgumentOutOfRangeException("depth", "The trim depth must not be negative.");
        }

        if (this.count == 0)
        {
            return;
        }

        if (depth == 0)
        {
            this.Clear();
        }
        else
        {
            var prevCount = this.count;
            this.count = this.Trim(this.root, depth - 1);
            if (prevCount != this.count)
            {
                this.version++;
            }
        }
    }

    private int Trim(SplayTreeNode node, int depth)
    {
        if (depth == 0)
        {
            node.LeftChild = null;
            node.RightChild = null;
            return 1;
        }
        else
        {
            int count = 1;

            if (node.LeftChild != null)
            {
                count += Trim(node.LeftChild, depth - 1);
            }

            if (node.RightChild != null)
            {
                count += Trim(node.RightChild, depth - 1);
            }

            return count;
        }
    }

    public ICollection<TKey> Keys
    {
        get { return new TiedList<TKey>(this, this.version, this.AsList(node => node.Key)); }
    }

    public ICollection<TValue> Values
    {
        get { return new TiedList<TValue>(this, this.version, this.AsList(node => node.Value)); }
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
        this.AsList(node => new KeyValuePair<TKey, TValue>(node.Key, node.Value)).CopyTo(array, arrayIndex);
    }

    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
        return new TiedList<KeyValuePair<TKey, TValue>>(this, this.version, this.AsList(node => new KeyValuePair<TKey, TValue>(node.Key, node.Value))).GetEnumerator();
    }

    private IList<TEnumerator> AsList<TEnumerator>(Func<SplayTreeNode, TEnumerator> selector)
    {
        if (this.root == null)
        {
            return new TEnumerator[0];
        }

        var result = new List<TEnumerator>(this.count);
        PopulateList(this.root, result, selector);
        return result;
    }

    private void PopulateList<TEnumerator>(SplayTreeNode node, List<TEnumerator> list, Func<SplayTreeNode, TEnumerator> selector)
    {
        if (node.LeftChild != null) PopulateList(node.LeftChild, list, selector);
        list.Add(selector(node));
        if (node.RightChild != null) PopulateList(node.RightChild, list, selector);
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }

    private sealed class SplayTreeNode
    {
        public readonly TKey Key;

        public TValue Value;
        public SplayTreeNode LeftChild;
        public SplayTreeNode RightChild;

        public SplayTreeNode(TKey key, TValue value)
        {
            this.Key = key;
            this.Value = value;
        }
    }

    [DebuggerDisplay("Count = {Count}")]
    private sealed class TiedList<T> : IList<T>
    {
        private readonly SplayTree<TKey, TValue> tree;
        private readonly int version;
        private readonly IList<T> backingList;

        public TiedList(SplayTree<TKey, TValue> tree, int version, IList<T> backingList)
        {
            if (tree == null)
            {
                throw new ArgumentNullException("tree");
            }

            if (backingList == null)
            {
                throw new ArgumentNullException("backingList");
            }

            this.tree = tree;
            this.version = version;
            this.backingList = backingList;
        }

        public int IndexOf(T item)
        {
            if (this.tree.version != this.version) throw new InvalidOperationException("The collection has been modified.");
            return this.backingList.IndexOf(item);
        }

        public void Insert(int index, T item)
        {
            throw new NotSupportedException();
        }

        public void RemoveAt(int index)
        {
            throw new NotSupportedException();
        }

        public T this[int index]
        {
            get
            {
                if (this.tree.version != this.version) throw new InvalidOperationException("The collection has been modified.");
                return this.backingList[index];
            }
            set
            {
                throw new NotSupportedException();
            }
        }

        public void Add(T item)
        {
            throw new NotSupportedException();
        }

        public void Clear()
        {
            throw new NotSupportedException();
        }

        public bool Contains(T item)
        {
            if (this.tree.version != this.version) throw new InvalidOperationException("The collection has been modified.");
            return this.backingList.Contains(item);
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            if (this.tree.version != this.version) throw new InvalidOperationException("The collection has been modified.");
            this.backingList.CopyTo(array, arrayIndex);
        }

        public int Count
        {
            get { return this.tree.count; }
        }

        public bool IsReadOnly
        {
            get { return true; }
        }

        public bool Remove(T item)
        {
            throw new NotSupportedException();
        }

        public IEnumerator<T> GetEnumerator()
        {
            if (this.tree.version != this.version) throw new InvalidOperationException("The collection has been modified.");

            foreach (var item in this.backingList)
            {
                yield return item;
                if (this.tree.version != this.version) throw new InvalidOperationException("The collection has been modified.");
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }
    }
}