I like about this solution, that it is good understandable and, with a bit above four seconds, fast(er than many other solutions).

a funny, it looks like I made it, but now I'm also running into the runtim error! I read about it earlier today, so I gotta speed it up somehow :´-D
Well, I gotta say that the higher katas are not only more sophisticated, but definitely also more time consuming!

yeah well, okay. Why make it harder than it is. Maybe it'll be just fine with a randomized approach. :-D

There is a Discord server dedicated to Loopover puzzle enthousiasts.

I also stumbled over the 4 kyu, but especially because it is mentioned being easier than the kata "A Simple Music Encoder" - which is 5 kyu.
"A Simple Music Encoder": https://www.codewars.com/kata/58db9545facc51e3db00000a

I would like to suggest to add a specific test case. My first solution got accepted sometimes, and sometimes not, dependent on the randomised test cases. In case of a range, followed by a single final digit, it generated an error. So it with this (shortened) input
[..., -59, -58, -57, -54]
it generated this (shortened) output
'...,-59--54'
instead of the correct output:
'...,-59--57,-54'

I would suggest to include this test case, so it is always tested.

Ah interesting kata. I spent quite some time on a structure, until I tried another structure that was easier. If you get stuck, I recommend you trying a different approach. ;-)

ahaha, I'm always curious, when I managed to solv it somehow, to see these one-liners! But I am wondering, is it also fast to write? I mean, condensing knowledge is quite a bit of a task! ;-)