You have to think about what they are trying to test. If it's "Do they know how to quickly find an answer to a known problem?", then your route is correct. If

You have to think about what they are trying to test. If it's "Do they know how to quickly find an answer to a known problem?", then your route is correct. If it's "Could they take a problem that hasn't been solved before and solve it themselves?", then you're not really demonstrating that. Unless I'm told otherwise, I would assume that a coding challenge would be more of the latter. Of course, it's not how you'd solve it in real life. But that's like saying you should be allowed a calculator in a mental maths exam because you'd never try to to 27324/623 in your head these days.