aoc/2024/04/p2/main.rs

use std::{
    cmp,
    fs::File,
    io::Read,
    time::{Duration, Instant},
};

fn main() -> std::io::Result<()> {
    let args: Vec<_> = std::env::args().collect();
    let filename = &args[1];
    let runs: u32 = args[2]
        .parse()
        .expect("did not receive a number as `runs` argument");

    let mut contents = vec![];
    let mut file = File::open(filename)?;
    file.read_to_end(&mut contents)?;
    let lines: Vec<_> = contents.split(|&b| b == b'\n').collect();

    let mut max = Duration::ZERO;
    let mut avg = Duration::ZERO;
    let mut min = Duration::MAX;
    let result = run(&lines);
    for i in 0..runs {
        let a = Instant::now();
        let run_result = run(&lines);
        let b = Instant::now();
        if result != run_result {
            panic!(
                "supposed result is {} but this run got {} after {} runs",
                result, run_result, i
            );
        }

        let d = b - a;
        max = cmp::max(d, max);
        min = cmp::min(d, min);
        avg += d / runs;
    }

    println!("\x1b[0;34mtotal \x1b[1;33m{result}\x1b[0;34m\n  runs  \x1b[1;33m{runs:?}\x1b[0;34m\n  avg.  \x1b[1;35m{avg:?}\x1b[0;34m\n  max.  \x1b[1;31m{max:?}\x1b[0;34m\n  min.  \x1b[1;32m{min:?}\x1b[0m");
    Ok(())
}

fn run(lines: &[&[u8]]) -> usize {
    let mut t = 0;
    for (i, ln) in lines.iter().enumerate() {
        'l: for (j, &ch) in ln.iter().enumerate() {
            if ch == b'A' {
                let mut passes = true;
                for chars in [(1, -1), (1, 1)].iter().map(|(y, x)| {
                    (
                        getdat(lines, (j, i), (*x, *y)),
                        getdat(lines, (j, i), (-*x, -*y)),
                    )
                }) {
                    let (Some(a), Some(b)) = chars else { continue 'l; };
                    if !((a == b'M' && b == b'S') || (a == b'S' && b == b'M')) {
                        passes = false;
                        break;
                    }
                }
                if passes { t += 1; }
            }
        }
    }
    t
}

macro_rules! pstve_try_none {
    ($a:expr, $b:expr) => {{
        let r = $a + $b;
        if r < 0 {
            return None;
        }
        r
    }};
}

fn getdat(buf: &[&[u8]], pos: (usize, usize), dir: (isize, isize)) -> Option<u8> {
    let new_1 = pstve_try_none!(pos.1 as isize, dir.1) as usize;
    let new_0 = pstve_try_none!(pos.0 as isize, dir.0) as usize;
    let ln = buf.get(new_1)?;
    let ch = ln.get(new_0)?;
    Some(*ch)
}