using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(CompressString("aaabccccdd"));

        Console.WriteLine(CompressString("yyyyyzzzzzzzzzz"));

        Console.WriteLine(CompressString("abcd"));

        Console.WriteLine(CompressString("hhhccchhhccc"));

​

​

        static string CompressString(string orginalInput)

        {

            if (string.IsNullOrWhiteSpace(orginalInput))

                return ""; // We can either return an empty string or throw an exception message.

                //throw new ArgumentException("Input value cannot be null or Empty");

​

            string input = string.Join("", orginalInput.Trim().ToLower().Split(' '));

​

            StringBuilder Result = new StringBuilder();

​

            char currentChar = input[0];

            int count = 1;

​

            for (int i = 1; i < input.Length; i++)

            {

                if (input[i] == currentChar)

                    count++;

                else

                {

                    Result.Append((count == 1) ? currentChar : $"{currentChar}{count}");

                    currentChar = input[i];

                    count = 1;

                }

            }

            Result.Append((count == 1) ? currentChar : $"{currentChar}{count}");

            return Result.ToString();

        }

    }

}