using System;

using System.Diagnostics;

using System.Collections.Generic;

using System.IO;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string text = @"rrr

ttt

​

yyyy

zzz

cc

iii

o";

        long elapsed = 0;

        Stopwatch sw = new Stopwatch();

        sw.Start();

        using (StringReader reader = new StringReader(text))

        {

            int i = 0; // create indexer

            Console.WriteLine(i.ToString() + ".");

            string line = string.Empty;

            while( (line = reader.ReadLine()) != null)

            {

                if(string.IsNullOrWhiteSpace(line))

                {

                    i++;

                    Console.WriteLine();

                    Console.WriteLine(i.ToString() + ".");

                }

                else

                {

                    Console.WriteLine(line);

                }

            }

        }

        elapsed = sw.ElapsedTicks;

        Console.WriteLine("my method took : " + elapsed);

        sw.Restart();

        MatchCollection findings = new Regex(@"((.|(\n.))+)|((\n\n)((.|(\n.))+))").Matches(text);

        for(int i = 0; i < findings.Count; i++) {

            int groupIndex = findings[i].Groups[1].Length > 0 ? 0 : 6;

            string match = findings[i].Groups[groupIndex].ToString();

            Console.WriteLine(i+".");

            Console.WriteLine(match);

        }

        elapsed = sw.ElapsedTicks;

        Console.WriteLine("your method took : " + elapsed);

    }

}