LinkedList`.cs

public class LinkedListNode<TNode>
{
    public TNode Value
    {
        get; 
        set;
    }
    
    public LinkedListNode<TNode> Next
    {
        get;
        set;
    } 

    public LinkedListNode(TNode value)
    {
        Value = value;
    }
}

public class LinkedList<TNode> : IEnumerable<TNode>
{
    public LinkedListNode<TNode> Head
    {
        get; 
        private set;
    }

    public LinkedListNode<TNode> Tail
    {
        get; 
        private set;
    }

    public int Count
    {
        get; 
        private set;
    }

    public void AddFirst(TNode value)
    {
        AddFirst(new LinkedListNode<TNode>(value));
    }

    public void AddFirst(LinkedListNode<TNode> node)
    {
        LinkedListNode<TNode> temp = Head;

        Head = node;

        node.Next = temp;

        Count += 1;

        if (Count == 1)
        {
            Tail = Head;
        }
    }

    public void AddLast(TNode value)
    {
        AddLast(new LinkedListNode<TNode>(value));
    }

    public void AddLast(LinkedListNode<TNode> node)
    {
        if (Count == 0)
        {
            Head = node;
        }
        else
        {
            Tail.Next = node;
        }

        Tail = node;

        Count += 1;
    }

    public void RemoveFirst()
    {
        if (Count != 0)
        {
            Head = Head.Next;
            Count -= 1;

            if (Count == 0)
            {
                Tail = null;
            }
        }
    }

    public void RemoveLast()
    {
        if (Count != 0)
        {
            if (Count == 1)
            {
                Head = null;
                Tail = null;
            }
            else
            {
                var current = Head;
                while (current.Next != Tail)
                {
                    current = current.Next;
                }
                current.Next = null;
                Tail = current;
            }

            Count -= 1;
        }
    }

    public bool Contains(TNode value)
    {
        return Enumerable.Contains(this, value);
    }

    public IEnumerator<TNode> GetEnumerator()
    {
        var current = Head;
        while (current != null)
        {
            yield return current.Value;
            current = current.Next;
        }
    }

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

    public void Clear()
    {
        Head = null;
        Tail = null;
        Count = 0;
    }
}