great solution

This is so effective, instead of double looping to create 2 lists...

You and I both. So much to learn. I love coming and seeing what the other's solutions are, it's almost like having hundreds of mentors seeing the different thought processes.

I forget how simple slices are, they can do so much yet I forget how great they are all the time.

this makes me feel funny

Very clean. I should have thought of this.

done, Completed in 1037.57ms :)

You're doing reduce(...) // reduce(...) for i in range(...), that's a nested loop, hence O(n^2).

You should post your solution in a comment so it could be reviewed. Maybe you're missing something, and your algorithm is not actually linear.

I made a linear solution, but it also fails the test .. maybe you could give advice? I have no one to ask, since I study everything on my own ..
I would also like to say this is clearly not level 6.
This task was worth devide into two, with and without a performance test.

Your second approach is correct, but the overall algorithm is bad. You have to make it fully linear.

too easy for 6 kyu