Maybe it has been suggested before, but what about a tournament-mode? Make users able to organize tournaments with private invitations. For example, users start with 0 points and a time limit, let's say 2 hours. Provide the ability to add a set of Katas which the users will have to solve during these 2 hours. The one who solves the most Katas during the period, wins! Would be great for group-seminars, workshops, etc.

(If there already exists possibilities for this, please inform me! :-))

Nevermind on the second part of my comment. I'm new to Codewars. I see this issue has already been remarked in the discourse section.

Are you not excluding the possibility here that when you are paid with a 100 dollar bill, you could give change if you have three 25 dollar bills? So scenario with input { 25, 25, 25, 100 } would fail with this code. I think the acceptance tests are incomplete.

Possibly more accepted code is may not take this scenario in account. Have not had time to review all code. Somebody should look into this.