@Blind4Basics Good question! :) Yes in fact the test class seems to be in the same package as the solution class, so the public method and class were accessible from the solution class. I have now made them non-public to prevent this. I wonder how many more devious ways there are to cheat this thing? :)

@Blind4Basics How would test methods being public be a problem?

Edited to shuffle the collection of test cases before testing them. Wouldn't want anyone cheating :)

OK added vector tag.