main.rs

const WIDTH: usize = 12;
const COUNT: usize = 1000;

pub fn main() {
    let gamma = include_str!("../input.txt")
        .lines()
        .map(|l| usize::from_str_radix(l, 2).unwrap())
        .fold(vec![0; WIDTH], |count, bits| {
            count
                .into_iter()
                .enumerate()
                .map(|(i, n)| n + ((bits & 1 << i) >> i))
                .collect()
        })
        .into_iter()
        .enumerate()
        .map(|(i, b)| ((b >= COUNT / 2) as u32) << i)
        .sum::<u32>();

    println!("{}", gamma * (!gamma & ((1 << WIDTH) - 1)));
}