Most likely because whoever wrote this didn't realize it can be solved in O(1). Or because this kata is listed in the section "LINQ excercises" so the author tried to solve it using System.Linq library. I don't think it can be solved in O(1) using language integrated query.

Then I see others' solution and realize just how bad my method is, and I forgot to remove that "just in case" floor replacement, too.

No need to convert to array.

Why use O(N) approach when it's a O(1) problem?

Or it was your code. Most probably that... Closing.

This happen on 9nd test
Traceback:
in
File "/usr/lib/python3.6/random.py", line 274, in shuffle
x[i], x[j] = x[j], x[i]
KeyError: 0

And after i put a print on the beginning of my code nothing appear so the test case maybe broke.

holy crap dude