You are one of the few who really checks whether the acceptance criteria are met, namely a maximum of 10 numbers and that each number is in the range from 0 to 9. Your code, like mine probably, may not look that cool single-line, but in practice it would survive any unit test. The 2 discounter tests of codewars are not to be taken seriously. The favored solution is wrong in my opinion, because there is no check of the input. Such a thing is in practice deadly. Therefore I find your solution very good.