Vector can be slow if you create and destroy them a lot, since they allocate. You can work around to some extent by providing a custom allocator, but using something like SmallVector or absl::InlinedVector can be much faster when the N is known.
Yeah, that's one of my biggest pet peeves when looking at other people's code (along with unnecessary dynamic allocations in general). One of the reasons I perhaps irrationally still prefer C++ to Rust is the pervasive use of dynamic arrays of known static size in the latter's documentation, and how it makes fixed-size arrays much less ergonomic to use than dynamic arrays.
I tried this at some points where I often have to allocate dynamic memory though I knew an upper bound (no static size, though). Got some nice (and easy) extra performance, thank you (and the others who replied to my comment) very much for the hint!
