using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
        string pattern = @"^((?(D)(?!))(?<C>1)|(?(D)(?!))(?<-C>0)|(?(C)(?!))(?<D>0)|(?(C)(?!))(?<-D>1))*(?(C)(?!))(?(D)(?!))$";

        string[] matchedStrings = new[] { "1100", "1010", "0101", "11000011" };
        string[] unmatchedStrings = new[] { "110", "001", "1100001" };

        foreach (var s in matchedStrings)            
            Console.WriteLine("Should matching {0}: {1}", s, Regex.IsMatch(s, pattern));
        foreach (var s in unmatchedStrings)
            Console.WriteLine("Should not matching {0}: {1}", s, !Regex.IsMatch(s, pattern));     
	}
}