Leetcode Variant-Plus N

Given a non-negative number represented as an array of digits, plus N to the number.

The digits are stored such that the most significant digit is at the head of the list.

N is guaranteed to be non-negative.

Solution:

 public class Solution {
     public int[] plusN(int[] digits, int n) {
         int carry = n;
         int index = digits.length-1;
         while (carry>0 && index>=0){
             int val = digits[index]+carry;
             carry = val/10;
             val = val%10;
             digits[index]=val;
             index--;
         }
         int[] res;
         if (index<0 && carry>0){
             String cStr = Integer.toString(carry);
             res = new int[cStr.length()+digits.length];
             for (int i=0;i<cStr.length();i++)
                 res[i]=cStr.charAt(i)-'0';
             for (int i=0;i<digits.length;i++)
                 res[i+cStr.length()]=digits[i];
         } else res = digits;
         return res;
     }
 }