day04.rs

use std::{fs};
use std::collections::HashMap;

pub(crate) fn day04() {
    println!("{}", part_a(fs::read_to_string("input/2023/day04/input.txt").unwrap()));
    println!("{}", part_b(fs::read_to_string("input/2023/day04/input.txt").unwrap()));
}

fn part_a(cards: String) -> i32 {
    cards.lines().map(|line| {
        let (_, numbers) = line.split_once(": ").unwrap();

        let (winning_s, right) = numbers.split_once(" | ").unwrap();

        let winning: Vec<i32> = winning_s.split_whitespace().map(|n| n.parse::<i32>().unwrap()).collect();

        let matches: Vec<i32> = right.split_whitespace()
            .map(|n| n.parse::<i32>().unwrap())
            .filter(|n| winning.contains(n))
            .collect();

        if matches.len() < 1 { return 0 }

        let mut ans = 1;
        for _ in 1..matches.len() {
            ans *= 2;
        }

        ans
    }).sum()
}

fn part_b(cards: String) -> usize {
    let mut ctr: HashMap<usize, usize> = HashMap::new();
    cards.lines().enumerate().map(|(i, line)| {
        let mult = *ctr.entry(i).or_insert(1);
        let (_, numbers) = line.split_once(": ").unwrap();

        let (winning_s, right) = numbers.split_once(" | ").unwrap();

        let winning: Vec<usize> = winning_s.split_whitespace().map(|n| n.parse::<usize>().unwrap()).collect();

        let matches: Vec<usize> = right.split_whitespace()
            .map(|n| n.parse::<usize>().unwrap())
            .filter(|n| winning.contains(n))
            .collect();

        for j in 1..=matches.len() {
            *ctr.entry(i + j).or_insert(1) += mult;
        }

        mult
    }).sum()
}

#[cfg(test)]
mod day04_tests {
    use std::fs;

    use crate::y2023::day04::{part_a, part_b};

    #[test]
    fn test_works() {
        assert_eq!(13, part_a(fs::read_to_string("input/2023/day04/test.txt").unwrap()));
        assert_eq!(30, part_b(fs::read_to_string("input/2023/day04/test_b.txt").unwrap()));
    }

    #[test]
    fn input_works() {
        assert_eq!(24175, part_a(fs::read_to_string("input/2023/day04/input.txt").unwrap()));
        assert_eq!(18846301, part_b(fs::read_to_string("input/2023/day04/input.txt").unwrap()));
    }
}