Day 4: Scratchcards


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  • capitalpb@programming.dev
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    11 months ago

    I enjoyed this one. It was a nice simple break after Days 1 and 3; the type of basic puzzle I expect from the first few days of Advent of Code. Pretty simple logic in this one, I don’t think I would change too much. I’m sure I’ll find a way to clean up how it’s written a bit, but I’m happy with this one today.

    https://github.com/capitalpb/advent_of_code_2023/blob/main/src/solvers/day04.rs

    struct Scratchcard {
        winning_numbers: HashSet,
        player_numbers: HashSet,
    }
    
    impl Scratchcard {
        fn from(input: &str) -> Scratchcard {
            let (_, numbers) = input.split_once(':').unwrap();
            let (winning_numbers, player_numbers) = numbers.split_once('|').unwrap();
            let winning_numbers = winning_numbers
                .split_ascii_whitespace()
                .filter_map(|number| number.parse::().ok())
                .collect::>();
            let player_numbers = player_numbers
                .split_ascii_whitespace()
                .filter_map(|number| number.parse::().ok())
                .collect::>();
    
            Scratchcard {
                winning_numbers,
                player_numbers,
            }
        }
    
        fn matches(&self) -> u32 {
            self.winning_numbers
                .intersection(&self.player_numbers)
                .count() as u32
        }
    }
    
    pub struct Day04;
    
    impl Solver for Day04 {
        fn star_one(&self, input: &str) -> String {
            input
                .lines()
                .map(Scratchcard::from)
                .map(|card| {
                    let matches = card.matches();
                    if matches == 0 {
                        0
                    } else {
                        2u32.pow(matches - 1)
                    }
                })
                .sum::()
                .to_string()
        }
    
        fn star_two(&self, input: &str) -> String {
            let cards: Vec = input.lines().map(Scratchcard::from).collect();
            let mut card_counts = vec![1usize; cards.len()];
    
            for card_number in 0..cards.len() {
                let matches = cards[card_number].matches();
    
                if matches == 0 {
                    continue;
                }
    
                for i in 1..=matches {
                    card_counts[card_number + i as usize] += card_counts[card_number];
                }
            }
    
            card_counts.iter().sum::().to_string()
        }
    }