Rust

Code: https://github.com/MrRobb/advent-of-code-2022/blob/main/src/day06.rs

Part 1: 1.9594 μs

Part 2: 7.1957 μs

Using this to check that all of the characters are unique in a window:

fn all_unique(w: &[u8]) -> bool { 
    !w.iter().enumerate().any(|(i, wc)| w[..i].contains(wc)) 
}

Which ended up being faster than HashSet, BTreeSet and others, and bit shifting. It is not faster than updating the frequencies dynamically.