I’ve read through the exercise again and now realise that my function won’t help you (that) much. Have to do to much in the office right now to solve that one for myself 
Looks like a fun task…
edit
As everyone went to dinner early and I have an appointement for dinner in an hour, I took the time to solve it.
Using a streamified version of my algorithm from above I finished the task in less than 5 minutes and a handfull of lines.
