There's a known problem with some of Rust kata. Rust version got recently updated on Codewars and now some kata do not compile correctly. They are being updated gradually, but there's still ~100 of them to go. I will try to get someone on this one, but I do not know when it will get fixed :( Just back up your code somewhere and try again tomorrow, or in a couple of days. Hopefully it will get processed until then.

It works on my end if I change the Rust version from 1.44 to 1.49. It's related to the rand crate dependency that introduced a breaking change.

Let me know if that resolves the issue.