Implement 2023 day 7 part 1

2023/src/day07.rs

@@ -1,7 +1,112 @@
-pub fn part1(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+use nom::bytes::complete::tag;
+use nom::bytes::complete::take;
+use nom::character::complete::newline;
+use nom::combinator::map_res;
+use nom::multi::many1;
+use nom::sequence::pair;
+use nom::sequence::terminated;
+use nom::IResult;
+
+use crate::common::parse_input;
+
+#[derive(PartialEq, Eq, PartialOrd, Ord)]
+enum Kind {
+    HighCard,
+    Pair,
+    TwoPair,
+    ThreeOfAKind,
+    FullHouse,
+    FourOfAKind,
+    FiveOfAKind,
+}
+
+impl<'a> From<&'a [u8; 5]> for Kind {
+    fn from(cards: &'a [u8; 5]) -> Self {
+        let mut counts = [0u8; 15];
+        for &card in cards {
+            counts[card as usize] += 1;
+        }
+
+        counts.sort_unstable();
+        match (counts[14], counts[13]) {
+            (5, _) => Kind::FiveOfAKind,
+            (4, _) => Kind::FourOfAKind,
+            (3, 2) => Kind::FullHouse,
+            (3, _) => Kind::ThreeOfAKind,
+            (2, 2) => Kind::TwoPair,
+            (2, _) => Kind::Pair,
+            _ => Kind::HighCard,
+        }
+    }
+}
+
+struct Hand {
+    cards: [u8; 5],
+    bid: u32,
+    kind: Kind,
+}
+
+fn parse_hands(i: &[u8]) -> IResult<&[u8], Vec<Hand>> {
+    fn map_card(c: u8) -> anyhow::Result<u8> {
+        Ok(match c {
+            d @ b'2'..=b'9' => d - b'0',
+            b'T' => 10,
+            b'J' => 11,
+            b'Q' => 12,
+            b'K' => 13,
+            b'A' => 14,
+            other => anyhow::bail!("Invalid card {other}"),
+        })
+    }
+
+    many1(map_res(
+        pair(
+            terminated(take(5usize), tag(" ")),
+            terminated(nom::character::complete::u32, newline),
+        ),
+        |(hand, bid)| -> anyhow::Result<Hand> {
+            let mut cards = [0; 5];
+            for (t, &s) in cards.iter_mut().zip(hand) {
+                *t = map_card(s)?
+            }
+            let kind = Kind::from(&cards);
+
+            Ok(Hand { cards, bid, kind })
+        },
+    ))(i)
+}
+
+pub fn part1(input: &[u8]) -> anyhow::Result<String> {
+    let mut hands = parse_input(input, parse_hands)?;
+
+    hands.sort_unstable_by(|first, second| {
+        first
+            .kind
+            .cmp(&second.kind)
+            .then_with(|| first.cards.cmp(&second.cards))
+    });
+
+    let sum: u64 = hands
+        .iter()
+        .enumerate()
+        .map(|(i, hand)| (i + 1) as u64 * u64::from(hand.bid))
+        .sum();
+
+    Ok(sum.to_string())
 }
 
 pub fn part2(_input: &[u8]) -> anyhow::Result<String> {
     anyhow::bail!("Not implemented")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/07.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "6440");
+    }
+}