Задача: Компрессия строки

CompressedStr.cs

using System;
using System.Text;
					
public class Program
{
	public static string CompressedStr(string str) {
		var res = new StringBuilder();
		int index = 0;

		while (index < str.Length)
		{
		    int count = 0;
		    var curr = str[index];

		    while(index < str.Length && count < 9 && str[index] == curr) {
			count++;
			index++;
		    }

		    res.Append(count).Append(curr);
		}

		return res.ToString();
	}
	
	public static void Main()
	{
		Console.WriteLine("UniLecs");
		
		// tests
		Console.WriteLine(CompressedStr("abcde")); // "1a1b1c1d1e"
		Console.WriteLine(CompressedStr("aaaaaaaaaaaaaabb")); // "9a5a2b"
	}
}