2023: Day 4

README.md

@@ -8,6 +8,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 01: Trebuchet?!](aoc_2023/src/day_01.rs)
 - [Day 02: Cube Conundrum](aoc_2023/src/day_02.rs)
 - [Day 03: Gear Ratios](aoc_2023/src/day_03.rs)
+- [Day 04: Scratchcards](aoc_2023/src/day_04.rs)
 
 ## [2022](https://adventofcode.com/2022) [![aoc_2022](https://github.com/Basicprogrammer10/advent-of-code/actions/workflows/aoc_2022.yml/badge.svg)](https://github.com/Basicprogrammer10/advent-of-code/actions/workflows/aoc_2022.yml)
 

aoc_2023/src/day_04.rs

@@ -0,0 +1,101 @@
+use common::{Answer, Solution};
+
+pub struct Day04;
+
+impl Solution for Day04 {
+    fn name(&self) -> &'static str {
+        "Scratchcards"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let cards = parse(input);
+        cards
+            .iter()
+            .map(|x| x.count_wins())
+            .filter(|x| *x > 0)
+            .map(|x| 2u32.pow(x.saturating_sub(1) as u32))
+            .sum::<u32>()
+            .into()
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        let cards = parse(input);
+
+        let mut queue = cards.clone();
+        let mut visited = 0;
+
+        while let Some(card) = queue.pop() {
+            let wins = card.count_wins();
+            visited += 1;
+            if wins == 0 {
+                continue;
+            }
+
+            let num = card.number as usize;
+            for i in num + 1..=num + wins {
+                queue.push(cards[i as usize - 1].clone());
+            }
+        }
+
+        visited.into()
+    }
+}
+
+#[derive(Clone)]
+struct Card {
+    number: u8,
+    winning: Vec<u8>,
+    scratch: Vec<u8>,
+}
+
+fn parse(input: &str) -> Vec<Card> {
+    let mut cards = Vec::new();
+    for line in input.lines() {
+        let (_, line) = line.split_once(": ").unwrap();
+        let (winning, scratch) = line.split_once(" | ").unwrap();
+        let parse = |s: &str| s.split_whitespace().map(|x| x.parse().unwrap()).collect();
+        cards.push(Card {
+            number: cards.len() as u8 + 1,
+            winning: parse(winning),
+            scratch: parse(scratch),
+        });
+    }
+
+    cards
+}
+
+impl Card {
+    fn count_wins(&self) -> usize {
+        self.scratch
+            .iter()
+            .filter(|x| self.winning.contains(x))
+            .count()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use common::Solution;
+    use indoc::indoc;
+
+    use super::Day04;
+
+    const CASE: &str = indoc! {"
+        Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+        Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+        Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+        Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+        Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+        Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day04.part_a(CASE), 13.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day04.part_b(CASE), 30.into());
+    }
+}

aoc_2023/src/lib.rs

@@ -5,12 +5,14 @@ mod aoc_lib;
 mod day_01;
 mod day_02;
 mod day_03;
+mod day_04;
 // [import_marker]
 
 #[rustfmt::skip]
 pub const ALL: &[&dyn Solution] = &[
     &day_01::Day01,
     &day_02::Day02,
     &day_03::Day03,
+    &day_04::Day04,
     // [list_marker]
 ];