pest

    
part1    =  { SOI ~ (mul_expr | junk)+ ~ EOI }
part2    =  { (enabled | disabled)+ ~ EOI }
mul_expr =  { "mul(" ~ number ~ "," ~ number ~ ")" }
number   =  { ASCII_DIGIT{1,3} }
junk     = _{ ASCII }
on       = _{ "do()" }
off      = _{ "don't()" }
enabled  = _{ (SOI | on) ~ (!(off) ~ (mul_expr | junk))+ }
disabled = _{ off ~ (!(on) ~ junk)+ }

  

 rust

    
use std::fs;

use color_eyre::eyre;
use pest::Parser;
use pest_derive::Parser;

#[derive(Parser)]
#[grammar = "memory.pest"]
pub struct MemoryParser;

fn parse(input: &str, rule: Rule) -> eyre::Result<usize> {
    let sum = MemoryParser::parse(rule, input)?
        .next()
        .expect("input must be ASCII")
        .into_inner()
        .filter(|pair| pair.as_rule() == Rule::mul_expr)
        .map(|pair| {
            pair.into_inner()
                .map(|num| num.as_str().parse::<usize>().unwrap())
                .product::<usize>()
        })
        .sum();
    Ok(sum)
}

fn part1(filepath: &str) -> eyre::Result<usize> {
    let input = fs::read_to_string(filepath)?;
    parse(&input, Rule::part1)
}

fn part2(filepath: &str) -> eyre::Result<usize> {
    let input = fs::read_to_string(filepath)?;
    parse(&input, Rule::part2)
}

fn main() -> eyre::Result<()> {
    color_eyre::install()?;

    let part1 = part1("d03/input.txt")?;
    let part2 = part2("d03/input.txt")?;
    println!("Part 1: {part1}\nPart 2: {part2}");
    Ok(())
}

  

 rust

    
use color_eyre::eyre;
use std::{fs, num, str::FromStr};

#[derive(Debug, PartialEq, Eq)]
struct Report(Vec<isize>);

impl FromStr for Report {
    type Err = num::ParseIntError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let v: Result<Vec<isize>, _> = s
            .split_whitespace()
            .map(|num| num.parse::<isize>())
            .collect();
        Ok(Report(v?))
    }
}

impl Report {
    fn is_safe(&self) -> bool {
        let ascending = self.0[1] > self.0[0];
        let (low, high) = if ascending { (1, 3) } else { (-3, -1) };
        self.0.windows(2).all(|w| {
            let a = w[0];
            let b = w[1];
            b >= a + low && b <= a + high
        })
    }

    fn is_dampsafe(&self) -> bool {
        if self.is_safe() {
            return true;
        }
        for i in 0..self.0.len() {
            let damped = {
                let mut v = self.0.clone();
                v.remove(i);
                Self(v)
            };
            if damped.is_safe() {
                return true;
            }
        }
        false
    }
}

fn main() -> eyre::Result<()> {
    color_eyre::install()?;

    let part1 = part1("d02/input.txt")?;
    let part2 = part2("d02/input.txt")?;
    println!("Part 1: {part1}\nPart 2: {part2}");
    Ok(())
}

fn part1(filepath: &str) -> eyre::Result<isize> {
    let mut num_safe = 0;
    for l in fs::read_to_string(filepath)?.lines() {
        if Report::from_str(l)?.is_safe() {
            num_safe += 1;
        }
    }
    Ok(num_safe)
}

fn part2(filepath: &str) -> eyre::Result<isize> {
    let mut num_safe = 0;
    for l in fs::read_to_string(filepath)?.lines() {
        if Report::from_str(l)?.is_dampsafe() {
            num_safe += 1;
        }
    }
    Ok(num_safe)
}