using System;

using System.Linq;

using System.IO;

using System.Runtime.Serialization.Formatters.Binary;

using System.Collections.Generic;

​

public class Program

{

​

    public static void Main()

    {

        var input = @"rrr

ttt

​

yyyy

zzz

cc

​

iii

o";

        var res = GetGroups(input.Split(Environment.NewLine.ToCharArray()));

        foreach(var r in res)

        {

            Console.WriteLine(string.Join(",",r));

        }

    }

    private static IEnumerable<IEnumerable<string>> GetGroups(IEnumerable<string> source)

    {

        var grouped = new List<string>();

        foreach(var el in source)

        {

            if(!string.IsNullOrEmpty(el))

                grouped.Add(el);

            else if(grouped.Any())

            {

                yield return grouped;

                grouped = new List<string>();

            }

        }

        if(grouped.Any())

            yield return grouped;

    }

}