this post was submitted on 03 Dec 2024
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Advent Of Code

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An unofficial home for the advent of code community on programming.dev!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2024

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Day 3: Mull It Over

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[โ€“] [email protected] 2 points 3 weeks ago (1 children)

Rust

Regex made this one pretty straightforward. The second part additionally looks for do() and don't() in the same regex, then we do a case distinction on the match.

use regex::{Regex, Captures};

fn mul_cap(cap: Captures) -> i32 {
    let a = cap.get(1).unwrap().as_str().parse::<i32>().unwrap();
    let b = cap.get(2).unwrap().as_str().parse::<i32>().unwrap();
    a * b
}

fn part1(input: String) {
    let re = Regex::new(r"mul\((\d{1,3}),(\d{1,3})\)").unwrap();
    let res = re.captures_iter(&input).map(mul_cap).sum::<i32>();
    println!("{res}");
}

fn part2(input: String) {
    let re = Regex::new(r"do\(\)|don't\(\)|mul\((\d{1,3}),(\d{1,3})\)").unwrap();
    let mut enabled = true;
    let mut res = 0;
    for cap in re.captures_iter(&input) {
        match cap.get(0).unwrap().as_str() {
            "do()" => enabled = true,
            "don't()" => enabled = false,
            _ if enabled => res += mul_cap(cap),
            _ => {}
        }
    }
    println!("{res}");
}

util::aoc_main!();
[โ€“] [email protected] 1 points 3 weeks ago

Our part1's are basically identical, but for part 2 I just regex deleted everything between dont() anddo() `, after sanitizing out the newlines.

I guess it would have failed if my test data had a mul after the last dont, but it worked out, so good enough :)