Your question is Next-Bigger Digit From Number. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How would you find the next biggest digit for a given integer by using the digits in the number?
Implement a function that returns the smallest integer greater than the input that can be formed by rearranging exactly the same digits. Explain the behavior when no greater arrangement exists, and address repeated digits, invalid input, and numbers with multiple digits.