Methods 8

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace _08.SumTwoArraysOfDigits
{
    class Program
    {
        static void Main(string[] args)
        {
            DateTime start = DateTime.Now;
            byte[] firstArray = { 9, 4, 1, 9 };
            byte[] secondArray = { 1, 5, 6, 7, 9, 9, 9 };

            string total = SumArrays(firstArray, secondArray);
            Console.WriteLine(total);
            DateTime final = DateTime.Now;
            Console.WriteLine("{0}", final - start);

        }

        private static string SumArrays(byte[] firstArray, byte[] secondArray)
        {
            List<byte> maxArray = new List<byte>();
            List<byte> minArray = new List<byte>();
            if (firstArray.Length>secondArray.Length)
            {
                maxArray.AddRange(firstArray);
                minArray.AddRange(secondArray);
            }
            else
            {
                maxArray.AddRange(secondArray);
                minArray.AddRange(firstArray);
            }

            int minLength = minArray.Count;
            int maxLength = maxArray.Count;
            int addition = 0;
            int sum;
            StringBuilder result = new StringBuilder();
            for (int i = 0; i < minLength; i++)
            {
                sum = minArray[i] + maxArray[i] + addition;
                if (sum>=10)
                {
                    addition = 1;
                    sum = sum % 10;
                    result.Append(sum);
                }
                else
                {
                    result.Append(sum);
                    addition = 0;
                }
            }

            for (int j = minLength; j < maxLength; j++)
            {
                sum =maxArray[j] + addition;
                if (sum >= 10)
                {
                    addition = 1;
                    sum = sum % 10;
                    result.Append(sum);
                }
                else
                {
                    result.Append(sum);
                    addition = 0;
                }
            }
            if (addition==1)
            {
                result.Append(1);
            }
            char[] reversed = (result.ToString()).ToCharArray();
            result.Clear();
            for (int i = reversed.Length-1; i >=0; i--)
            {
                result = result.Append(reversed[i]);
            }
            return result.ToString();
        }
    }
}