"Clarity before performance". O(2n) vs O(nlgn), where do you lose your performance?

Maintainability is more important than performance is most cases. Even more so when we are talking about small amounts of data in a tiny program. If you make a loop that has to go through a gigantic list of entries, then sure I'll agree.

That aside, I don't know any Python at all. This is just the solustion for the translation that was submitted.

The best solution here in terms of performance, only iterates onces over the list.

I don't like this solution, you put clarity before performance.

Your solution loops 3 times through the list when you can make in just once