advent_2025/src/main.rs

use std::{
    fs::File,
    io::{BufRead as _, BufReader},
};

fn get_lines(name: &str) -> impl Iterator<Item = String> {
    BufReader::new(File::open(name).unwrap())
        .lines()
        .map(|line| line.unwrap())
}

mod day1 {
    use std::collections::HashMap;

    use crate::get_lines;

    #[allow(dead_code)]
    pub fn task1() {
        let mut a = Vec::<i32>::new();
        let mut b = Vec::<i32>::new();
        for line in get_lines("input.txt") {
            let (a1, b1) = line.trim_end().split_once("   ").unwrap();
            a.push(a1.parse().unwrap());
            b.push(b1.parse().unwrap());
        }
        a.sort_unstable();
        b.sort_unstable();
        let result: i32 = a.into_iter().zip(b).map(|(a, b)| (a - b).abs()).sum();
        println!("{result}");
    }

    #[allow(dead_code)]
    pub fn task2() {
        let mut a = Vec::<u32>::new();
        let mut b = HashMap::<u32, u32>::new();
        for line in get_lines("input.txt") {
            let (a1, b1) = line.trim_end().split_once("   ").unwrap();
            a.push(a1.parse().unwrap());
            *b.entry(b1.parse().unwrap()).or_insert(0) += 1;
        }
        let result: u32 = a.into_iter().map(|a| a * *b.get(&a).unwrap_or(&0)).sum();
        println!("{result}");
    }
}

mod day2 {
    use itertools::Itertools;

    use crate::get_lines;

    fn safe(iter: impl Iterator<Item = i32>) -> bool {
        let mut order = None;
        for (a, b) in iter.tuple_windows() {
            if !(1..4).contains(&(a - b).abs()) {
                return false;
            }
            if order.is_none() {
                order = Some(a.cmp(&b));
            } else if order != Some(a.cmp(&b)) {
                return false;
            }
        }
        true
    }

    fn parse_line(line: &str) -> impl Iterator<Item = i32> + '_ {
        line.trim()
            .split(' ')
            .map(|num| num.parse::<i32>().unwrap())
    }

    #[allow(dead_code)]
    pub fn task1() {
        let result = get_lines("input.txt")
            .filter(|line| safe(parse_line(line)))
            .count();
        println!("{result}");
    }

    #[allow(dead_code)]
    pub fn task2() {
        let result = get_lines("input.txt")
            .filter(|line| {
                let numbers = parse_line(line).collect_vec();
                if safe(numbers.iter().copied()) {
                    return true;
                }
                let mut test = Vec::with_capacity(numbers.len() - 1);
                for i in 0..numbers.len() {
                    test.extend_from_slice(&numbers[..i]);
                    test.extend_from_slice(&numbers[i + 1..]);
                    if safe(test.iter().copied()) {
                        return true;
                    }
                    test.clear();
                }
                false
            })
            .count();
        println!("{result}");
    }
}

fn main() {
    // day1::task1();
    // day1::task1();
    day2::task1();
    day2::task2();
}