From ed8137d599a687fc842fc135bd2ecdf680d0e427 Mon Sep 17 00:00:00 2001
From: Lars Martens <lars@martens.red>
Date: Mon, 4 Dec 2023 12:38:07 +0100
Subject: [PATCH] Solve day 4

---
 input/04-test |  6 +++++
 src/bin/04.rs | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 input/04-test
 create mode 100644 src/bin/04.rs

diff --git a/input/04-test b/input/04-test
new file mode 100644
index 0000000..71f208a
--- /dev/null
+++ b/input/04-test
@@ -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
\ No newline at end of file
diff --git a/src/bin/04.rs b/src/bin/04.rs
new file mode 100644
index 0000000..1a9f6cc
--- /dev/null
+++ b/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()
+}