Hi; there are a few things not working with your solution, but the main one is that you are print rather than returnint your solution.

Furthermore, currently you are printing for j in ls several different times, whereas you will need to find a way to return only once - maybe by building up an output string then returning once it is finished. Hope that helps you get started on debugging!

Scala description needs update: the description claims you must return false for invalid input, but the tests expect an empty string.

Returning empty string is more sensible behaviour, please update the description to reflect this.