what the hell is happening in that list comprehension? How is the range(a,b) constructed if a,b are defined in a child loop?

you can also just use {} braces instead of [] to directly create a set comprehension without the need of converting the list with set()

The best solution that I've seen so far

Returning -1 to show that the question has no interest... Anyway too late to changeit now.

It would still error in python 2 as he said his list length is 2 and this is hard coded to 5.

This should simply ask how many times it passes the window and that's it. Returning -1 for cases when the answer is really 0 seems odd.