66.Plus One

Given a non-negative integer represented as anon-emptyarray of digits, plus one to the integer.

You may assume the integer do not contain any leading zero, except the number 0 itself.

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

class Solution {
    // 999 -> 1000
    public int[] plusOne(int[] digits) {
        if (digits == null) {
            return new int[0];
        }
        if (digits.length == 0) {return digits;}

        int sum = 1;  
        for (int i = digits.length - 1; i >= 0; i--) {
            int temp = digits[i] + sum;
            digits[i] = temp % 10;
            sum  = temp / 10; 
        }
        if (sum != 0) {
            int[] ans = new int[digits.length + 1];
            ans[0] = sum;
            for (int i = 0; i < digits.length; i++) {
                ans[i+1] = digits[i];
            }
            return ans;
        }else{
           return digits;
        }

    }
}