C# FreeList

FreeList.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace FreeListClass
{
	public class FreeList<T>
	{
		private class FreeListItem<T>
		{
			public int Previous { get; set; }
			public int Next { get; set; }
			public T Value { get; set; }

			public FreeListItem(int previous, int next)
			{
				Previous = previous;
				Next = next;
			}
		}

		List<FreeListItem<T>> items;

		public int allocatedIndexTail = -1;
		public int unallocatedIndexHead = 0;

		public FreeList(int capacity = 10)
		{
			items = new List<FreeListItem<T>>();
			for (int i = 0; i < capacity - 1; ++i)
			{
				items.Add(new FreeListItem<T>(i - 1, i + 1));
			}
			items.Add(new FreeListItem<T>(capacity - 2, -1));
		}

		public FreeListNode<T> Add(T value)
		{
			if (items[unallocatedIndexHead].Next == -1)
			{
				items.Add(new FreeListItem<T>(unallocatedIndexHead, -1));
				items[unallocatedIndexHead].Next = items.Count - 1;
			}
			if (allocatedIndexTail == -1)
			{
				allocatedIndexTail = unallocatedIndexHead;
				unallocatedIndexHead = items[unallocatedIndexHead].Next;
				items[allocatedIndexTail].Next = -1;
				items[unallocatedIndexHead].Previous = -1;
			}
			else
			{
				items[allocatedIndexTail].Next = unallocatedIndexHead;
				items[unallocatedIndexHead].Previous = allocatedIndexTail;
				allocatedIndexTail = items[allocatedIndexTail].Next;
				unallocatedIndexHead = items[unallocatedIndexHead].Next;
				items[allocatedIndexTail].Next = -1;
				items[unallocatedIndexHead].Previous = -1;
			}
			return new FreeListNode<T>(this, allocatedIndexTail);
		}

		public void Remove(int index)
		{
			FreeListItem<T> value = items[index];
			items[unallocatedIndexHead].Previous = index;
			if (value.Next != -1)
			{
				items[value.Next].Previous = value.Previous;
			}
			if (value.Previous != -1)
			{
				items[value.Previous].Next = value.Next;
			}
			if (allocatedIndexTail == index)
			{
				allocatedIndexTail = value.Previous;
			}
			value.Next = unallocatedIndexHead;
			unallocatedIndexHead = index;
			value.Previous = -1;
		}
	}
}

FreeListNode.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace FreeListClass
{
	public class FreeListNode<T>
	{
		public FreeList<T> FreeList { get; set; }
		public int Index { get; set; }

		public FreeListNode(FreeList<T> freeList, int index)
		{
			FreeList = freeList;
			Index = index;
		}

		public void Remove()
		{
			FreeList.Remove(Index);
		}
	}
}

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace FreeListClass
{
	class Program
	{
		static void Main(string[] args)
		{
			FreeList<int> foo = new FreeList<int>();
			foo.Add(0);
			foo.Remove(0);
		}
	}
}