using System;

using System.Text.RegularExpressions;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var inputText = "C234,,MD43,,5678,asdf,$#$&#," + Environment.NewLine + ",,,3423,2278,1212,,,,";

        var sanitizedInput = Regex.Replace(inputText, @"[^,0-9a-zA-Z]+", "");

        var rawItems = sanitizedInput.ToUpper().Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);

        var newString = string.Join(",", rawItems.Distinct());

        Console.WriteLine(newString);

    }

}