As of writing this the top-ranked solutions on Google are for the 3.0.0 release of rustlings. They also contain bugs that would fail the updated test suites in rustlings 4.4.0.
Check out the rustings repo to get started.
I'm just getting started with learning Rust. Of course these solutions all compile and pass the rustlings test suites for 4.4.0, but you might be able to write more ideomatic code. PR's are welcome if that's the case. Rust is also a fast moving language, so by the time you're reading this there may be more elegant ways to solve some of the problems.
I'll endeavor to update this repo for any new releases of rustlings; make sure the version you're working on matches the version in this repo for best results.