using System;
using System.Text;

namespace Amazon.RunLength
{
    class Program
    {
        static void Main(string[] args)
        {
            var content = @"AAAABBCCDAA";
            var result = Encode(content);
            Console.WriteLine(@"{0}:{1}", content, result);

            var encrypted = @"4A2B2C1D2A10F";
            var decrypted = Decode(encrypted);
            Console.WriteLine(@"{0}:{1}", encrypted, decrypted);
        }

        static string Encode(string content)
        {
            const string format = @"{0}{1}";
            if (string.IsNullOrWhiteSpace(content))
                return string.Empty;

            var sb = new StringBuilder();
            var current = 0;
            var item = content[current];
            var i = current+1;
            for(; i < content.Length; i++) {
                if(content[i] == item)
                    continue;

                sb.AppendFormat(format, i - current, item);
                item = content[i];
                current = i;
            }

            sb.AppendFormat(format, i - current, item);

            return sb.ToString();
        }

        static string Decode(string content) {
            var sb = new StringBuilder();
            for(var i = 0; i < content.Length;){
                var current = 0;
                while(Char.IsDigit(content[i + current]))
                    current += 1;


                var times = int.Parse(content.Substring(i, current));
                sb.Append(new String(content[i+current], times));

                i += current + 1;
            }

            return sb.ToString();
        }
    }
}