Advent of Code 2021 - Day 10: Syntax Scoring

syntax_scoring.rs

fn parse(subsystem: Vec<Vec<char>>) -> u64 {
    subsystem
        .iter()
        .map(|line| {
            if let (Some(c), _) = check_line(line) {
                match c {
                    ')' => 3,
                    ']' => 57,
                    '}' => 1197,
                    '>' => 25137,
                    _ => panic!("Invalid token!"),
                }
            } else {
                0
            }
        })
        .sum()
}

fn autocomplete(subsystem: Vec<Vec<char>>) -> u64 {
    let mut scores = subsystem
        .iter()
        .map(|line| check_line(line))
        .filter(|(error, _)| error.is_none())
        .map(|(_, stack)| {
            stack.iter().rev().fold(0, |total, &c| {
                total * 5
                    + match c {
                        '(' => 1,
                        '[' => 2,
                        '{' => 3,
                        '<' => 4,
                        _ => panic!("Invalid token!"),
                    }
            })
        })
        .collect::<Vec<_>>();

    scores.sort_unstable();
    scores[scores.len() / 2]
}

fn check_line(line: &[char]) -> (Option<char>, Vec<char>) {
    let mut stack = Vec::new();

    for &c in line {
        match c {
            '(' | '[' | '{' | '<' => stack.push(c),
            _ => match stack.pop().unwrap() {
                '(' if c == ')' => continue,
                '[' if c == ']' => continue,
                '{' if c == '}' => continue,
                '<' if c == '>' => continue,
                _ => return (Some(c), stack),
            },
        }
    }

    (None, stack)
}