add 04

04/src/main.rs

@@ -0,0 +1,86 @@
+use std::collections::HashSet;
+
+use itertools::Itertools;
+
+fn main() {
+    let cards = aoc::read_file("input.txt")
+        .into_iter()
+        .map(Card::from_line)
+        .collect_vec();
+
+    part_a(&cards);
+    part_b(&cards);
+}
+
+fn part_a(cards: &[Card]) {
+    let mut sum = 0;
+
+    for card in cards {
+        let count = card.winning.intersection(&card.have).count() as u32;
+
+        if count == 0 {
+            continue;
+        }
+
+        let value = 2_usize.pow(count - 1);
+        sum += value;
+    }
+
+    println!("{sum}");
+}
+
+fn part_b(cards: &[Card]) {
+    let mut result = 0;
+    let mut register = vec![0_usize; cards.len()];
+
+    for card in cards.iter() {
+        let mut card_count = card.matching_numbers_count();
+
+        let additional_counts = 1 + register.pop().unwrap();
+
+        let mut j = 0;
+        let length = register.len();
+        while card_count != 0 {
+            register[length - j - 1] += additional_counts;
+            card_count -= 1;
+            j += 1;
+        }
+
+        result += additional_counts;
+    }
+
+    println!("{result}");
+}
+
+struct Card {
+    winning: HashSet<u8>,
+    have: HashSet<u8>,
+}
+
+impl Card {
+    fn new(winning: HashSet<u8>, have: HashSet<u8>) -> Self {
+        Self { winning, have }
+    }
+
+    fn from_line(line: String) -> Self {
+        let stripped = line.split_once(':').unwrap().1;
+        let (winning_raw, have_raw) = stripped.split_once('|').unwrap();
+
+        let winning = process_raw_numbers(winning_raw);
+
+        let have = process_raw_numbers(have_raw);
+
+        Self::new(winning, have)
+    }
+
+    fn matching_numbers_count(&self) -> usize {
+        self.winning.intersection(&self.have).count()
+    }
+}
+
+fn process_raw_numbers(numbers: &str) -> HashSet<u8> {
+    numbers
+        .split_whitespace()
+        .map(|number| number.parse().unwrap())
+        .collect()
+}