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2023: Day 4, part 2
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parent
1a76994a15
commit
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1 changed files with 26 additions and 2 deletions
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@ -10,6 +10,8 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
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let mut points = Vec::new();
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let card_count = input.trim().lines().count().try_into()?;
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let mut copies = vec![0; card_count];
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for line in input.lines() {
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if line.is_empty() {
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continue;
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@ -17,6 +19,12 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
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let (fst, mine) = line.split_once(" | ").ok_or("expected |")?;
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let (fst, winning) = fst.split_once(": ").ok_or("expected :")?;
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let (_, card) = fst.split_once(' ').ok_or("expected ' '")?;
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let card = card
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.trim()
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.parse()
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.ok()
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.and_then(|n: usize| n.checked_sub(1))
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.ok_or("invalid card number")?;
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let mine = mine
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.split(' ')
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.filter(|s| !s.is_empty())
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@ -28,14 +36,30 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
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.map(|n| n.parse())
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.collect::<Result<HashSet<u32>, _>>()?;
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let count: u32 = winning.intersection(&mine).count().try_into().unwrap();
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let count = winning.intersection(&mine).count();
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if count > 0 {
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points.push(2_u64.pow(count - 1));
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points.push(2_u64.pow((count - 1).try_into()?));
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}
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// part 2 calculations
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// add the current card to the count
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copies[card] += 1;
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let instances = copies[card];
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// add 'count' copies of subsequent cards
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let next_card = card + 1;
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(next_card..next_card + count).for_each(|n| {
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if let Some(entry) = copies.get_mut(n) {
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*entry += instances;
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}
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});
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}
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let total_points: u64 = points.iter().sum();
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let total_cards: u64 = copies.iter().sum();
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println!("Part 1: {}", total_points);
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println!("Part 2: {}", total_cards);
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Ok(())
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}
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