… but that's an interview. If you cannot, within the time, demonstrate any ability, why should you be hired?
The question above, as clarified, is not complicated, nor does it rely on memorization or some "trick": anyone purporting to be a SWE should be able to write an essentially de novo solution to it.
(And in my own technical interviews, there are multiple questions, to specifically hedge against any one being "that one question a good candidate is going to miss because it's just not their day". It doesn't happen: it's either all or nothing.)
