@SpandexTiger, I just solved it and I also found it hard to understand for a couple of hours. But reading some of the first comments from this kata (between Blind4Basics and Johan) should help you understand how to calculate the oddness (without those comments I wouldn't have been able to complete it xD).

It is one of the great underappreciated kata's. In time, these get Legendary status.

I wish that too. It was originally not even supposed to be a puzzle, but people kept perceiving it as such.

Can we let it be now? I'm not changing it anyway. It is what it is, and opinions are divided. Feel free to vote your conscience.

that means if there is no match
(which will result in null)
return empty array.

can you explain the || here?

yes)