advent-of-code/2022/day3/rust/src/main.rs

use std::{
    collections::HashSet,
    io::{stdin, Read},
};

fn item_priority(item: char) -> u32 {
    match item {
        'a'..='z' => item as u32 - 'a' as u32 + 1,
        'A'..='Z' => item as u32 - 'A' as u32 + 27,
        _ => panic!("invalid item {item}"),
    }
}

struct Rucksack {
    left: HashSet<char>,
    right: HashSet<char>,
}

fn main() {
    let mut data = String::new();
    stdin().read_to_string(&mut data).unwrap();

    let sacks: Vec<_> = data
        .lines()
        .map(|line| {
            let (left, right) = line.split_at(line.len() / 2);
            assert_eq!(left.len(), right.len());

            let left: HashSet<_> = left.chars().collect();
            let right: HashSet<_> = right.chars().collect();

            Rucksack { left, right }
        })
        .collect();

    let sum1: u32 = sacks
        .iter()
        .map(|sack| item_priority(*sack.left.intersection(&sack.right).next().unwrap()))
        .sum();

    let sum2: u32 = sacks
        .chunks(3)
        .into_iter()
        .map(|sacks| {
            let common = sacks
                .iter()
                .map(|sack| &sack.left | &sack.right)
                .reduce(|a, b| &a & &b)
                .unwrap();
            assert_eq!(common.len(), 1);

            item_priority(common.into_iter().next().unwrap())
        })
        .sum();

    println!("{}", sum1);
    println!("{}", sum2);
}