so what does "compressibility of the next sequence" even mean?

• edit: so it means being able to group 3 or more adjacent numbers to a sequence

Ok, thanks for the reply!
So this means that: (notice how only the last digit changes in the inputs)

• 1234321234321235 gives 123 => 432 => 123 => 432 => 123 => 5
• 1234321234321234 gives 1234 => 321 => 234 => 321 => 234

and we could produce examples arbitrarily long with only the last digits that differs while the output is completely different.

I mean that's interesting but it's a tiny bit more challenging to implement than I first thought! :D

Assuming the first choice doesn't affect compressibility of the next sequence, it's 12345 => 43 => 234, so the assumption is wrong.
Assuming the first choice does affect compressibility of the next sequence, it's 1234 => 543 => 234, so the assumption is right.
So it's 1:4+1,5:3-1,2:3+1.
The description isn't really a strict definition and could be improved, but the only ambiguities I've managed to find are related to borders between sequences of length 1 and 2, but the result is the same anyway in those cases.

What is [1, 2, 3, 4, 5, 4, 3, 2, 3, 4] supposed to return?

"1:5+1,4:3-1,3,4" or "1:4+1,5:3-1,2:3+1"?

Thanks!