Array Sum (InterviewBit)

public class Solution {

    public int[] addArrays(int[] A, int[] B) {

        int n1 = A.length;
        int n2 = B.length;

        int carry = 0;

        // StringBuffer to store the result
        StringBuffer sb = new StringBuffer();

        // Initialize indices for array traversal from right to left
        int i = n1-1;
        int j = n2-1;

        // Variable to store the next digit in the sum (from right to left)
        int nextDigit = 0;

        // Continue the loop until both arrays are completely traversed and there is no carry left
        while(i >= 0 || j >= 0 || carry > 0){

            // Extract digits from each array
            // if i or j becomes less than 0, that means no remaining digits are present for it
            // but the other number or even carry might still have some value
            int d1 = i<0 ? 0 : A[i];
            int d2 = j<0 ? 0 : B[j];

            // Calculate the sum of digits and the carry for the next iteration
            int s = d1 + d2 + carry;

            nextDigit = s % 10;   // this will be the next digit to be added
            carry = s / 10;       // Update carry for the next iteration

            // Insert the digit at the beginning of the result buffer
            sb.insert(0, String.valueOf(nextDigit));

            // Move to the next digits in both arrays
            i--; j--;
        }

        // Convert the result from StringBuffer to an array of integers
        int[] ans = new int[sb.length()];
        for(int k = 0; k < sb.length(); k++){
            ans[k] = Integer.parseInt(sb.charAt(k) + "");
        }

        return ans;
    }
}