I couldn't approve because of merge conflicts in the description so I forked your translation and upgraded the tests to JUnit 5.

I wanted to test efficiency out of all things

But the efficienty of what? calculations? building a string? There are several entangled tasks in your kata that might interact about the efficiency.

For now, there is no need for actual performances, in the way that any implementation that isn't doing something wrong about the time complexity will pass. Which is not a bad thing because on this kind of task, you cannot go that much further without entering the dreaded world of microoptimizations (this kind of kata is generally bad). But so, the difficulty is rather low.

cheers

When you are trying to solve this with exp you are overcomplicating things.

then kyu 6 seems spot on

At the moment, I have ranked it 7 with "somewhat satisfied". The math is not that hard, but figuring out 'k' was. I had to look for that formula online. Is it on purpose left out to find online?
If you can confirm it is possible to determine 'k' from the specification, I'll update my score.

not the one you wrote in the "complete solution" tab. But if you use a verification function in the test cases, yes, it will be run during the tests and will affect the runtime, so.

Note: to be perfectly clear: your "complete solution", as an author, isn't affecting the solution of another user who's completing the kata.

Yours, as in "kata author's"?