Not a specific kata issue, please raise it in Github if encountered again!

What exactly does the i+ do? I'm not quite getting it..

Hi, I've passed the tests and submitted the kata, and it shows up as completed for me. However, solutions are not unlocked, I get the following message:
"Since you have not yet solved this kata we have hidden the solutions from you. If you choose to view the solutions you will forfeit your eligibility to earn honor/rank progress for this kata."

Also, I'm not convinced my solution would work with an input list with > 3 lists which have repeats in non-adjacent lists.
Would you consider adding some test cases for that situation?