day9.rs

use std::env;
use std::fs::File;
use std::io::Read;

#[derive(Copy, Clone, Debug, Default)]
struct State {
    level: usize,
    in_garbage: bool,
    ignore_next: bool,
}

fn part1(input: &str) {
    let state = State::default();
    let (_, score) = input.chars().fold(
        (state, 0),
        |(state, score), item| match (item, state) {
            ('{', State {in_garbage: false, ignore_next: false, ..}) => (State {level: state.level + 1, ..state}, score),
            ('}', State {in_garbage: false, ignore_next: false, ..}) => (State {level: state.level - 1, ..state}, score + state.level),
            ('<', State {in_garbage: false, ignore_next: false, ..}) => (State {in_garbage: true, ..state}, score),
            ('>', State {in_garbage: true, ignore_next: false, ..}) => (State {in_garbage: false, ..state}, score),
            ('!', State {ignore_next: false, ..}) => (State {ignore_next: true, ..state}, score),
            (_, State {ignore_next: true, ..}) => (State {ignore_next: false, ..state}, score),
            _ => (state, score),
        },
    );

    println!("part 1: {}", score);
}

fn part2(input: &str) {
    let state = State::default();
    let (_, count) = input.chars().fold(
        (state, 0),
        |(state, count), item| match (item, state) {
            ('<', State {in_garbage: false, ignore_next: false, ..}) => (State {in_garbage: true, ..state}, count),
            ('>', State {in_garbage: true, ignore_next: false, ..}) => (State {in_garbage: false, ..state}, count),
            ('!', State {ignore_next: false, ..}) => (State {ignore_next: true, ..state}, count),
            (_, State {ignore_next: true, ..}) => (State {ignore_next: false, ..state}, count),
            (_, State {in_garbage: true, ..}) => (state, count + 1),
            _ => (state, count),
        },
    );

    println!("part 2: {}", count);
}

fn main() {
    let filename = env::args().nth(1).expect("filename");
    let mut file = File::open(filename).expect("file");
    let mut input = String::new();
    file.read_to_string(&mut input).expect("input");

    part1(&input);
    part2(&input);
}