Advent of Code 2023 Day 5 Part 2

main.rs

#[derive(Default)]
struct Map {
    dst: u64,
    src: u64,
    range: u64
}

#[derive(Default)]
struct Seed {
    start: u64,
    len: u64
}

#[derive(Default)]
struct Almanac {
    seeds: Vec<Seed>,
    maps: [Vec<Map>; 7]
}

fn is_digit(c: u8) -> bool {
    return c >= b'0' && c <= b'9';
}

fn get_almanac() -> Almanac {
    let mut almanac: Almanac = Default::default();
    let data = std::fs::read("input").unwrap();

    let mut i = 0;
    while data[i] != b':' {
        i += 1;
    }
    i += 2;

    'seeds: loop {
        let mut seed: Seed = Default::default();
        assert!(is_digit(data[i]));
        while is_digit(data[i]) {
            seed.start *= 10;
            seed.start += (data[i] - b'0') as u64;
            i += 1;
        }
        i += 1;
        assert!(is_digit(data[i]));
        while is_digit(data[i]) {
            seed.len *= 10;
            seed.len += (data[i] - b'0') as u64;
            i += 1;
        }
        almanac.seeds.push(seed);
        while !is_digit(data[i]) {
            if data[i] == b':' {
                i += 2;
                break 'seeds;
            }
            i += 1;
        }
    }

    let mut m = 0;
    loop {
        let mut map: Map = Default::default();
        assert!(is_digit(data[i]));
        while is_digit(data[i]) {
            map.dst *= 10;
            map.dst += (data[i] - b'0') as u64;
            i += 1;
        }
        i += 1;
        assert!(is_digit(data[i]));
        while is_digit(data[i]) {
            map.src *= 10;
            map.src += (data[i] - b'0') as u64;
            i += 1;
        }
        i += 1;
        assert!(is_digit(data[i]));
        while is_digit(data[i]) {
            map.range *= 10;
            map.range += (data[i] - b'0') as u64;
            i += 1;
        }
        almanac.maps[m].push(map);
        assert!(data[i] == b'\n');
        i += 1;
        if i >= data.len() {
            assert!(m == 6);
            break;
        }
        if data[i] == b'\n' {
            m += 1;
            if m > 6 {
                break;
            }
            while !is_digit(data[i]) {
                i += 1;
            }
        }
    }

    return almanac;
}

fn main() {
    let almanac = get_almanac();
    let mut answer = u64::MAX;
    for seed in almanac.seeds {
        for mut key in seed.start..seed.start + seed.len {
            for map in &almanac.maps {
                for m in map {
                    if key >= m.src && key < m.src + m.range {
                        key = (key - m.src) + m.dst;
                        break;
                    }
                }
            }
            answer = core::cmp::min(answer, key);
        }
    }
    println!("Answer: {answer}");
}