Solve day 4

src/bin/04.rs

@@ -0,0 +1,74 @@
+use std::collections::HashSet;
+
+const INPUT: &str = include_str!("../../input/04");
+const TEST_INPUT: &str = include_str!("../../input/04-test");
+
+fn main() {
+    assert_eq!(part1(TEST_INPUT), 13);
+    println!("Part 1: {}", part1(INPUT));
+    assert_eq!(part2(TEST_INPUT), 30);
+    println!("Part 2: {}", part2(INPUT));
+}
+
+fn part1(input: &str) -> u64 {
+    parse_cards(input).map(|card| card.score()).sum()
+}
+
+fn part2(input: &str) -> u64 {
+    let mut cards: Vec<Card> = parse_cards(input).collect();
+
+    for i in 0..cards.len() {
+        let winning = cards[i].count_winning();
+        for win in 1..=winning {
+            let win = i + win;
+            if win < cards.len() {
+                cards[win].copies += cards[i].copies;
+            }
+        }
+    }
+
+    cards.iter().map(|card| card.copies).sum()
+}
+
+#[derive(Clone)]
+struct Card {
+    copies: u64,
+    winning: HashSet<u64>,
+    owned: HashSet<u64>,
+}
+
+impl Card {
+    fn count_winning(&self) -> usize {
+        self.winning.intersection(&self.owned).count()
+    }
+
+    fn score(&self) -> u64 {
+        let got_winning = self.count_winning();
+        if got_winning > 0 {
+            2u64.pow(got_winning as u32 - 1)
+        } else {
+            0
+        }
+    }
+
+    fn parse(line: &str) -> Self {
+        let (_id, line) = line.split_once(": ").unwrap();
+        let (winning, owned) = line.split_once(" | ").unwrap();
+
+        Self {
+            copies: 1,
+            winning: parse_numbers(winning),
+            owned: parse_numbers(owned),
+        }
+    }
+}
+
+fn parse_cards(input: &str) -> impl Iterator<Item = Card> + '_ {
+    input.lines().map(Card::parse)
+}
+
+fn parse_numbers(line: &str) -> HashSet<u64> {
+    line.split_ascii_whitespace()
+        .map(|n| n.parse().unwrap())
+        .collect()
+}