Great solution!

actual: Some([-79472, 1796079, 3671538])

expect: Some([-79465, 1796045, 3671565])

Looks like a bug in the test suite?

.cloned() is a more convenient way of doing .map(Clone::clone) :)

Finally another recursive solution.

Which is IMO the only sensible thing to do, considering that the return type isn't an optional.

@Renaissance8905: I use guard any time I can to escape early. In this case, the return arr is an early escape in case times equals zero. So I don't only use guard in failure cases, but edge cases in general.

The added benefit here is that we don't have to scan the guard body for a return statement, since the compiler enforces it.

Nice! I like this solution a lot, but I'd use guard rather than if :)

You're using reduce where you could (and IMO should) have just used map :)