Only 4 fixed assertions in the entire test suite is insufficient code coverage - either increase the number of distinct fixed assertions to at least 20 (ideally including some edge cases as well) or write 100+ random tests (or do both ;) )

Keep in mind, you should not convert the arrays to numeric or other types and back throughout the solution.

If you want the Kata to be solved using a certain approach then enforce it in the Submit tests - just telling the solver "please use this approach" or "please don't use that language feature" will not stop solvers from coming up with alternative approaches. This can be achieved by reading the file /home/codewarrior/solution.txt and examining its contents.