Oh I see. A matter of the expected return type - I would put this to an issue of a poor description. Will update when I have time and will pull the problem in the mean time.

Yea, description needs work, was published not in full - will most likely unpub to allow me to update it. Also, Java streams solves the problem the same way - but I figured it would be a fun lower level problem that could be solved also by people that don't know how to use things like streams.

Good thoughts, will work on that.

I am able to execute all tests. Can you share your solution?