day4/src/main.rs

use std::collections::HashMap;

fn main() {
    let input = include_str!("../input.txt");

    let mut scores = vec![];
    let mut scratchcards: HashMap<usize, usize> = HashMap::new();

    let mut index = 0;

    for card in input.split('\n') {
        if card == "" {
            continue;
        }

        index += 1;

        let data = card.split(": ").collect::<Vec<_>>()[1];

        let [ winner_str, our_str ] = data.split('|').collect::<Vec<_>>()[..] else { panic!("Invalid card") };

        let mut winners: Vec<u8> = vec![];
        let mut ours: Vec<u8> = vec![];

        for num in winner_str.split(' ') {
            if num.is_empty() {
                continue;  // there are some double-spaces in the cards
            }

            winners.push(num.parse().unwrap());
        }

        println!("- the winning numbers are {:?}", winners);

        for num in our_str.split(' ') {
            if num.is_empty() {
                continue;  // there are some double-spaces in the cards
            }

            ours.push(num.parse().unwrap());
        }

        println!("- our numbers are {:?}", ours);

        let mut n = 0;
        for num in ours {
            if winners.contains(&num) {
                println!("  - {} is a winner!", num);
                n += 1
            }
        }

        if n != 0 {
            let score = 2_usize.pow(n - 1);
            scores.push(score);
            println!("Card {} has {} winning numbers, scoring it {} points!", index, n, score);

            let factor = scratchcards.get(&index).unwrap_or(&0) + 1;
            println!("- Adding {} cards to each of the next {} numbers", factor, n);
            for i in index+1..index + 1 + TryInto::<usize>::try_into(n).unwrap() {
                let old_copies = scratchcards.get(&i).unwrap_or(&0);
                println!("  - Adding {} cards to the {} that were already in card {}", factor, old_copies, i);
                scratchcards.insert(i, old_copies + factor);
            }
        } else {
            println!("This card didn't win at all, better luck next time...");
        }
    }

    println!("The total score was {}", scores.iter().sum::<usize>());

    let clones: usize = scratchcards.into_values().sum();
    println!("You have {} scratchcard clones, plus the original {}, which leaves you with a total of {}", clones, index, clones + index);
}