Envío 6481

Código

import java.util.*;
import java.lang.*;
import java.io.*;

class Main {

    public static void main(String[] args) throws java.lang.Exception {
        Scanner sc = new Scanner(System.in);

        String number = sc.nextLine();
        String v[] = number.split("");
        ArrayList<Integer> list = new ArrayList<>();
        for (int i = 0; i < number.length(); i++) {
            list.add(Integer.parseInt(v[i]));
        }
        int digit = sc.nextInt();
        System.out.println(sumOne(list,digit));
    }

    public static String sumOne(ArrayList<Integer> list, int digit) {

        int sum = list.get(list.size()-1)+ digit;
        int carry = sum/10;
        list.set(list.size()-1,sum%10);
        for (int i = list.size()-2; i >= 0; i--) {
            sum = list.get(i)+carry;
             
            list.set(i,sum%10);
            carry=sum/10;
            if(carry==0) return listToString(list, carry);
        }
        
        return listToString(list, carry);
    }

    public static String listToString(ArrayList<Integer> list, int carry) {
        StringBuilder st = carry!=0 ? new StringBuilder(carry): new StringBuilder();
        for (int numb : list) {
            st.append(numb);
        }
        return st.toString();
    }
}