just in time for bedtime

src/day4.rs

@@ -1,12 +1,14 @@
 use std::collections::HashSet;
 use std::fs;
 
+use itertools::Itertools;
+
 pub fn run() {
     println!("Day 4:");
     let input = fs::read_to_string("./inputs/day4.txt").expect("Could not read file");
 
     println!("\tPart 1: {}", part1(&input));
-    // println!("\tPart 2: {}", part2(&input));
+    println!("\tPart 2: {}", part2(&input));
 }
 
 fn part1(cards: &str) -> usize {
@@ -35,8 +37,33 @@ fn part1(cards: &str) -> usize {
     total_wins
 }
 
-fn part2(schematic: &str) -> usize {
-    todo!()
+fn part2(cards: &str) -> usize {
+    let number_of_cards: usize = cards.lines().collect::<Vec<_>>().len();
+    let mut card_wins = vec![0; number_of_cards];
+
+    for (current_card_number, card) in cards.lines().enumerate() {
+        let (_, card_numbers) = card.split_once(':').unwrap();
+        let (winners_raw, chances_raw) = card_numbers.split_once('|').unwrap();
+
+        let winners = winners_raw
+            .split(' ')
+            .filter(|s| !s.is_empty())
+            .map(|win| win.trim().parse::<usize>().unwrap())
+            .collect::<HashSet<usize>>();
+        let chances = chances_raw
+            .split(' ')
+            .filter(|s| !s.is_empty())
+            .map(|chance| chance.trim().parse::<usize>().unwrap())
+            .collect::<HashSet<usize>>();
+
+        let wins = winners.intersection(&chances).count();
+
+        for index in 1..=wins {
+            card_wins[index + current_card_number] += 1 + card_wins[current_card_number];
+        }
+    }
+
+    card_wins.iter().sum::<usize>() + number_of_cards
 }
 
 #[cfg(test)]
@@ -64,6 +91,6 @@ 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";
 
-        assert_eq!(part2(input), 467835);
+        assert_eq!(part2(input), 30);
     }
 }