using System;

​

public class Program

{

    public static void Main()

    {

        /*byte[] f = new byte[] { 1, 1, 1 };

        byte[] s = new byte[] { 255, 0, 255 };*/

        Random rand = new Random();

        int n = 2000;

        byte[] f = new byte[n];

        byte[] s = new byte[n];

        for (int i = 0; i < n; i++)

        {

            f[i] = (byte)rand.Next(0, 256);

            s[i] = (byte)rand.Next(0, 256);

        }

        byte[] result = AddRecursive(f, s);

        f.Print("f");

        s.Print("s");

        result.Print("Total result");

    }

​

    public static byte[] AddRecursive(byte[] f, byte[] s)

    {

        int n = f.Length;

        if (n == 0)

            return new byte[0];

        int sum = f[0] + s[0];

        if (n == 1)

        {

            if (sum > 255)

                return new byte[] { 1, (byte)(sum - 256) };

            else

                return new byte[] { 0, (byte)(sum) }; 

        }

        byte[] result = AddRecursive(f.Slice(1), s.Slice(1));

        sum += result[0];

        if (sum > 255)

        {

            return new byte[] { 1, (byte)(sum - 256)}.Concat(result.Slice(1));;

        }

        else

        {

            return new byte[] { 0, (byte)(sum)}.Concat(result.Slice(1));

        }

    }

}

​

public static class ArrayExtensions

{

    public static byte[] Slice(this byte[] array, int startIndex)

    {

        if (startIndex > array.Length)

            throw new ArgumentException("Invalid startIndex");

        byte[] result = new byte[array.Length - startIndex];

        Array.Copy(array, startIndex, result, 0, result.Length);

        return result;

    }

    public static byte[] Concat(this byte[] first, byte[] second)

    {

        byte[] result = new byte[first.Length + second.Length];

        first.CopyTo(result, 0);

        second.CopyTo(result, first.Length);

        return result;

    }

    public static void Print(this byte[] array, string arrayName)

    {

        Console.WriteLine(arrayName + ": [" + String.Join(", ", array) + "]");

    }

}