Double Linked List C# example

gistfile1.cs

public static void Main()
{
    	DoubleLinkedList list = new DoubleLinkedList();
	list.Insert("1");
	list.Insert("2");
	list.Insert("3");
	
	DoubleLink link4 = list.Insert("4");
	list.Insert("5");
	Console.WriteLine("List: " + list);
	
	list.InsertAfter(link4, "[4a]");
	Console.WriteLine("List: " + list);
	Console.Read();
}

public class DoubleLink
{
    public string Title { get; set; }
	public DoubleLink PreviousLink { get; set; }
	public DoubleLink NextLink { get; set; }

	public DoubleLink(string title)
	{
		Title = title;
	}

	public override string ToString()
	{
		return Title;
	}
}

public class DoubleLinkedList
{
	private DoubleLink _first;
	public bool IsEmpty
	{
		get
		{
			return _first == null;
		}
	}
	public DoubleLinkedList()
	{
		_first = null;
	}

	public DoubleLink Insert(string title)
	{
		// Creates a link, sets its link to the first item and then makes this the first item in the list.
		DoubleLink link = new DoubleLink(title);
		link.NextLink = _first;
		if (_first != null)
			_first.PreviousLink = link;
		_first = link;
		return link;
	}

	public DoubleLink Delete()
	{
		// Gets the first item, and sets it to be the one it is linked to
		DoubleLink temp = _first;
		if (_first != null)
		{
			_first = _first.NextLink;
			if (_first != null)
				_first.PreviousLink = null;
		}
		return temp;
	}

	public override string ToString()
	{
		DoubleLink currentLink = _first;
		StringBuilder builder = new StringBuilder();
		while (currentLink != null)
		{
			builder.Append(currentLink);
			currentLink = currentLink.NextLink;
		}
		return builder.ToString();
	}

	///// New operations
	public void InsertAfter(DoubleLink link, string title)
	{
		if (link == null || string.IsNullOrEmpty(title))
			return;
		DoubleLink newLink = new DoubleLink(title);
		newLink.PreviousLink = link;
		// Update the 'after' link's next reference, so its previous points to the new one
		if (link.NextLink != null)
			link.NextLink.PreviousLink = newLink;
		// Steal the next link of the node, and set the after so it links to our new one
		newLink.NextLink = link.NextLink;
		link.NextLink = newLink;
	}
}

I made a version that removes from the end for personal use:

		public class DoubleLink
		{
			public string Title { get; set; }
			public DoubleLink PreviousLink { get; set; }
			public DoubleLink NextLink { get; set; }
			public DoubleLink(string title){ Title = title; }
		}

		public class DoubleLinkedList
		{
			private DoubleLink _first;
			private DoubleLink _last; 
			private int _length;
			
			public int length() { return _length; }
			
			public DoubleLinkedList()
			{
				_first = null;
				_last = null;
				_length = 0;
			}

			public DoubleLink unshift(string title)
			{
				// Creates a link, sets its link to the first item and then makes this the first item in the list.
				DoubleLink link = new DoubleLink(title);
				link.NextLink = _first;
				if (_first != null) _first.PreviousLink = link;
				_first = link;
				if (_last == null) _last = link;
				_length ++;
				return link;
			}

			public DoubleLink shift()
			{
				// Gets the first item, and sets it to be the one it is linked to
				DoubleLink temp = _first;
				if (_first != null)
				{
					_first = _first.NextLink;
					if (_first != null)
						_first.PreviousLink = null;
				}
				_length = Math.Max(0, _length - 1);
				return temp;
			}
			
			public DoubleLink pop()
			{
				// Gets the last item, and sets it to be the one it is linked to
				DoubleLink temp = _last;
				if (_last != null)
				{
					_last = _last.PreviousLink;
					if (_last != null)
						_last.NextLink = null;
				}
				_length = Math.Max(0, _length - 1);
				return temp;
			}

			public override string ToString()
			{
				DoubleLink currentLink = _first;
				StringBuilder builder = new StringBuilder();
				while (currentLink != null)
				{
					builder.Append(currentLink.Title);
					currentLink = currentLink.NextLink;
				}
				return builder.ToString();
			}

		 
		}