Advent of Code - adventofcode.com

Bitsets ftw

#[inline]
fn unique(s: &[u8], n: usize) -> bool {
    s.iter()
        .fold(0u32, |acc, &c| acc | (1u32.wrapping_shl(c as u32)))
        .count_ones()
        == n as u32
}

fn solve(inp: &[u8], n: usize) -> usize {
    if let Some((i, _)) = inp.windows(n).enumerate().find(|(_, win)| unique(win, n)) {
        i + n
    } else {
        unreachable!()
    }
}

pub fn part1(inp: &[u8]) -> usize {
    solve(inp, 14)
}

pub fn part2(inp: &[u8]) -> usize {
    solve(inp, 14)
}