What exactly did he do here?

beatifull!
as somone that trying to study programing, i think the probblem with python is that in an excerice like this one, instead of study "how to think"- go over an array with a loop, and think what you need to do to replace somthing, python do it for you

:)

how did you come up with this?

I'm a bit surprised that this one isn't among the top rated.

For this, it would be possible to implement the girlfriend's task .. For example, 2.4.5.7.8

I'd say easy or hard depends on using certain data structures to help with the task.

3.43 µs ± 26.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

17 µs ± 143 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

I checked, his decision is almost 2 times faster in time.

I think it's hard for 7kyu

hack:)

what? o_O