//Will Maxwell
//wjmaxwel
//estimated time: 2 hours
//actual time: 3 hours

//package program4; //package for netbeans
import java.util.Scanner;
import java.lang.Integer;
import java.lang.Character;

public class Program4
{
    public static void main(String[] args)
    {
        Scanner keyboard = new Scanner(System.in);
        char[] arrayOne, arrayTwo, reverseArrayOne, reverseArrayTwo, arrayOneWithZeroes, arrayTwoWithZeroes, sum;
        String stringOne, stringTwo;
        int arrayLengthOne, arrayLengthTwo, maxLength;

        System.out.print("First number: ");
        stringOne = keyboard.nextLine();
        System.out.print("Second number: ");
        stringTwo = keyboard.nextLine();

        arrayOne = stringOne.toCharArray();
        arrayTwo = stringTwo.toCharArray();

        arrayLengthOne = stringOne.length();
        arrayLengthTwo = stringTwo.length();
        maxLength = max(arrayLengthOne, arrayLengthTwo);

        arrayOneWithZeroes = zeroes(arrayOne, arrayLengthOne);
        arrayTwoWithZeroes = zeroes(arrayTwo, arrayLengthTwo);

        reverseArrayOne = reverse(arrayOneWithZeroes, arrayLengthOne);
        reverseArrayTwo = reverse(arrayTwoWithZeroes, arrayLengthTwo);

        sum = add(arrayOneWithZeroes, arrayTwoWithZeroes, arrayLengthOne, arrayLengthTwo);
        sum = unzero(sum, maxLength);
        sum = reverse(sum, sum.length);
        System.out.print("Sum: ");
        System.out.println(sum);



    }

    public static char[] reverse(char[] array, int arrayLength) //reverse the array so addition algorithm is easier
    {
        int left = 0;
        int right = arrayLength - 1;

        while(left < right)
        {
            char temp = array[left];
            array[left] = array[right];
            array[right] = temp;
            left++;
            right--;
        }

        return array;

    }

    public static char[] add(char[] arrayOne, char[] arrayTwo, int lengthOne, int lengthTwo)
    {
        char[] sum = new char[20];
        int firstNum, secondNum, smallSum;
        boolean carry = false;

        for(int i = 0; i < 20; i++)
        {
            firstNum = (Integer.valueOf(arrayOne[i]) - 48); //48 is the offset of the ASCII value
            secondNum = (Integer.valueOf(arrayTwo[i]) - 48);
            smallSum = firstNum + secondNum;
            if(carry == true)
            {
                smallSum++;
            }
            carry = false;
            if(smallSum >= 10)
            {
                smallSum = smallSum%10;
                carry = true;
            }
            sum[i] = Character.forDigit(smallSum, 10);
        }

        return sum;
    }

    public static char[] zeroes(char[] array, int length) //adds zeroes to the empty spots in the array to make addition easier.
    {
        char[] arrayWithZeroes = new char[20];
        for(int i = 0; i < 20; i++)
        {
            if(i >= length)
            {
                arrayWithZeroes[i] = '0';
            }
            else
            {
                arrayWithZeroes[i] = array[i];
            }
        }

        return arrayWithZeroes;
    }

    public static char[] unzero(char[] array, int length) //takes off the padded zeroes
    {
        char[] unzero = new char[20];
        for(int i = 0; i < 20; i++)
        {
            if(i < length)
            {
                unzero[i] = array[i];
            }
        }
        if(array[length] != '0')
        {
            unzero[length] = array[length];
        }
        return unzero;
    }

    public static int max(int a, int b)
    {
        if(a > b)
        {
            return a;
        }
        else
        {
            return b;
        }
    }

}