private List<Integer> multiplyDigit(List<Integer> l, int digit) {
            List<Integer> result = new ArrayList<Integer>();
            int carry = 0;
            for (int i : l) {
                result.add((i * digit + carry) % 10);
                carry = (i * digit + carry) / 10;
            }
            if (carry != 0) {
                result.add(carry);
            }
            return result;
        }