I managed, not without difficulty, to find a solution to this Kata!
But I can't get past the random tests...
Code Wars gives me a timeout before the tests are finished.
I didn't use a brute force algorithm; the algorithm solves a puzzle in an average of 1ms, so I don't know what more I can do...
(Tests done in JS.)

I think it's because of the asynchronous nature of my tests, but I don't know how to fix it... Does anyone have any ideas?

Thank you for the feedback. The issue has been resolved.