using System;

using System.Text.RegularExpressions;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var goodList = new List<string>{"1", "12", "12 34","12 a 34", "1a", "54b", "32 c", "43-23", "45c/34", "45/34d", "67 / 345", "23a / 56", "12 / 56b"};

        var badList = new List<string>{"1 3 5", "34 a a", "34b s", "234a/a", "34b 456s", "34b/456s", "34b / 456s"};

        var pattern = @"^\d+[\s]?[a-z\W]?[\s]?[\W]?[\s]?\d+?[a-z]?$";

        var regex = new Regex(pattern);

        Console.WriteLine("Good list");

        Console.WriteLine("-------------");

        foreach (var item in goodList)

        {

            Console.WriteLine(string.Format("{0} - {1}", regex.IsMatch(item), item));

        }

​

        Console.WriteLine();

        Console.WriteLine("Bad list");

        Console.WriteLine("-------------");

        foreach (var item in badList)

        {

            Console.WriteLine(string.Format("{0} - {1}", regex.IsMatch(item), item));

        }

    }

}