using System.Collections.Generic;

using System;

#nullable enable

​

SortedList<string, int> l = new(new RomanNumeralComparer())

{

    // shuffled on purpose

    { "V", 5 },

    { "I", 1 },

    { "L", 50 },

    { "X", 10 },

};

​

​

// correctly prints in the order of 

// I V X L

foreach (var c in l)

{

    Console.WriteLine(c);

}

​

// big class for something so small

public class RomanNumeralComparer : IComparer<string>

{

    private readonly string _order = "IVXL";

​

    public int Compare(string? x, string? y)

    {

        if (x is null && y is null)

        {

            return 0;

        }

​

        if (x is null)

        {

            return -1;

        }

​

        if (y is null)

        {

            return 1;

        }

​

        int xRank = _order.IndexOf(x, StringComparison.InvariantCulture);

        int yRank = _order.IndexOf(y, StringComparison.InvariantCulture);

​

        return (xRank < yRank) ? -1 : (xRank == yRank) ? 0 : 1;

    }

}