using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var binaryString = "1100110010";

        var substrings = GetSubstringsFrom(binaryString);

        Console.WriteLine(string.Join(Environment.NewLine, substrings));

    }

    private static IEnumerable<string> GetSubstringsFrom(string source)

    {

        for (var i = 0; i < source.Length - 1; i++)

        {

            var equalDigitCount = source

                .Skip(i)

                .TakeWhile(letter => letter == source[i])

                .Count();

            var totalDigitCount = 2 * equalDigitCount;

            if (i + totalDigitCount > source.Length)

            {

                continue;

            }

            var remainingDigits = source

                .Skip(i + equalDigitCount)

                .Take(equalDigitCount);

            if (remainingDigits.Distinct().Count() > 1)

            {

                continue;

            }

            yield return source.Substring(i, totalDigitCount);

        }

    }

}

​