Rust Day 4 Part 2

rust/Cargo.lock

@@ -4,4 +4,4 @@ version = 3
 
 [[package]]
 name = "advent-of-code"
-version = "23.4.1"
+version = "23.4.2"

rust/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "advent-of-code"
-version = "23.4.1"
+version = "23.4.2"
 edition = "2021"
 default-run = "day04"
 

rust/src/day04/part_2.rs

@@ -1,5 +1,69 @@
-pub(crate) fn part_2(_input: &'static str) -> u64 {
-    todo!("Part 2")
+use std::collections::HashSet;
+
+struct Card {
+    times_won: usize,
+    numbers: HashSet<u8>,
+    winning_numbers: HashSet<u8>,
+}
+
+impl Card {
+    fn winning_number_count(&self) -> usize {
+        HashSet::intersection(&self.numbers, &self.winning_numbers).count()
+    }
+}
+
+pub(crate) fn part_2(input: &'static str) -> usize {
+    let prefix_end = input.find(':').expect("Input should start with 'Card  X:'") + 1;
+    let mut cards = input
+        .lines()
+        .map(|line| {
+            let mut number_groups = line[prefix_end..].split('|').map(|group| {
+                group
+                    .split(' ')
+                    .filter_map(|number| {
+                        if number.is_empty() {
+                            None
+                        } else {
+                            Some(
+                                number
+                                    .trim()
+                                    .parse::<u8>()
+                                    .expect("Every number should be a valid u8"),
+                            )
+                        }
+                    })
+                    .collect()
+            });
+            let numbers = number_groups
+                .next()
+                .expect("There should be two groups of numbers");
+
+            let winning_numbers = number_groups
+                .next()
+                .expect("There should be two groups of numbers");
+
+            assert!(
+                number_groups.next().is_none(),
+                "There should be no more groups of numbers"
+            );
+
+            Card {
+                times_won: 1,
+                numbers,
+                winning_numbers,
+            }
+        })
+        .collect::<Vec<_>>();
+
+    for idx in 0..cards.len() {
+        let card_score = cards[idx].winning_number_count();
+
+        for winning_idx in (idx + 1)..(idx + 1 + card_score) {
+            cards[winning_idx].times_won += cards[idx].times_won;
+        }
+    }
+
+    cards.iter().map(|card| card.times_won).sum()
 }
 
 #[cfg(test)]
@@ -8,17 +72,11 @@ mod tests {
 
     #[test]
     fn test_with_sample_solution() {
-        assert_eq!(
-            super::part_2(SAMPLE_INPUT),
-            todo!("Add result from example part 2")
-        );
+        assert_eq!(super::part_2(SAMPLE_INPUT), 30);
     }
 
     #[test]
     fn test_with_solution() {
-        assert_eq!(
-            super::part_2(crate::INPUT),
-            todo!("Add result for solved part 2")
-        );
+        assert_eq!(super::part_2(crate::INPUT), 5659035);
     }
 }