day(04): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

samples/day04.txt

@@ -0,0 +1,6 @@
+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

src/bin/day04.rs

@@ -0,0 +1,92 @@
+use std::{collections::HashSet, str::FromStr};
+
+use aoc_2023::*;
+
+type Output1 = i32;
+type Output2 = Output1;
+
+struct Card {
+    winning: HashSet<i32>,
+    draw: Vec<i32>,
+}
+
+impl FromStr for Card {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut parts = s.split(':').nth(1).unwrap().split('|');
+
+        let winning = parts
+            .next()
+            .unwrap()
+            .split_ascii_whitespace()
+            .map(|n| n.parse().unwrap())
+            .collect();
+        let draw = parts
+            .next()
+            .unwrap()
+            .split_ascii_whitespace()
+            .map(|n| n.parse().unwrap())
+            .collect();
+
+        Ok(Card { winning, draw })
+    }
+}
+
+impl Card {
+    fn matching(&self) -> usize {
+        self.draw
+            .iter()
+            .filter(|card| self.winning.contains(card))
+            .count()
+    }
+
+    fn score(&self) -> i32 {
+        let mut matched = 0;
+
+        for card in &self.draw {
+            if self.winning.contains(card) {
+                matched += 1;
+            }
+        }
+
+        if matched > 1 {
+            1 << (matched - 1)
+        } else {
+            matched
+        }
+    }
+}
+
+struct Day04 {
+    cards: Vec<Card>,
+}
+impl Solution<Output1, Output2> for Day04 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        let cards = file_to_structs(pathname);
+
+        Self { cards }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        self.cards.iter().map(Card::score).sum()
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        let mut counts = vec![1; self.cards.len()];
+
+        for (i, card) in self.cards.iter().enumerate() {
+            for j in 1..=card.matching() {
+                counts[i + j] += counts[i];
+            }
+        }
+
+        counts.iter().sum()
+    }
+}
+
+fn main() -> Result<()> {
+    Day04::main()
+}
+
+test_sample!(day_04, Day04, 13, 30);