C# equivalent of LinkedHashMap [duplicate]

Answer 1

I wrote this one, worked well enough for me in the past. Let me know if you find a mistake.

using System;
using System.Collections.Generic;

class LinkedHashMap<T, U>
{
    Dictionary<T, LinkedListNode<Tuple<U, T>>> D = new Dictionary<T, LinkedListNode<Tuple<U, T>>>();
    LinkedList<Tuple<U,T>> LL = new LinkedList<Tuple<U, T>>();

    public U this[T c]
    {
        get
        {
            return D[c].Value.Item1;
        }

        set
        {
            if(D.ContainsKey(c))
            {
                LL.Remove(D[c]);
            }

            D[c] = new LinkedListNode<Tuple<U, T>>(Tuple.Create(value, c));
            LL.AddLast(D[c]);
        }
    }

    public bool ContainsKey(T k)
    {
        return D.ContainsKey(k);
    }

    public U PopFirst()
    {
        var node = LL.First;
        LL.Remove(node);
        D.Remove(node.Value.Item2);
        return node.Value.Item1;
    }

    public int Count
    {
        get
        {
            return D.Count;
        }
    }
}

class LinkedHashMapTest 
{
    public static void Test()
    {
        var lhm = new LinkedHashMap<char, int>();

        lhm['a'] = 1;
        lhm['b'] = 2;
        lhm['c'] = 3;


        Console.WriteLine(lhm['a']);
        Console.WriteLine(lhm['b']);
        Console.WriteLine(lhm['c']);

        Console.WriteLine(lhm.PopFirst());
        Console.WriteLine(lhm.PopFirst());
        Console.WriteLine(lhm.PopFirst());
    }
}