using System;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    private static string CleanString(string text)

    {

        var validchars = "-_abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        var cleanstring = text.Replace(" ", "-"); // replace spaces with hyphens

        cleanstring = Regex.Replace(cleanstring, "-+", "-"); // replace repeating hyphens with a single hyphen

        cleanstring = cleanstring.ToLower(); // lowercase the string

        cleanstring = string.Join("", cleanstring.Where(x => validchars.Contains(x))); // remove invalid chars

        cleanstring = cleanstring.Trim('-'); // trim hyphens off the end

        return cleanstring;

    }

​

    public static void Main()

    {

        Console.WriteLine(CleanString("__- 123 Prof- -Alexander Law {MR} (MR) [MR]"));

    }

}