O(n). I'm proud of this one.

Fair enough. I did it in C++ and learned a bit from it.

For a Rust translation, you'll have to wait for someone else to write one, or you could solve this kata in other language and create the translation yourself.

Please add a Rust option. I'm learning it, and I've just done the Tribonacci problem, and I believe my solution was generic enough that it'll work on this one with minimal modifications.

Same :(