1 files changed, 169 insertions, 0 deletions
diff --git a/2023/src/bin/day_7.rs b/2023/src/bin/day_7.rs
new file mode 100644
index 0000000..3b629bd
--- /dev/null
+++ b/2023/src/bin/day_7.rs
@@ -0,0 +1,169 @@
+use nom::{
+    branch::alt,
+    character::complete::{char as nom_char, line_ending, space1, u32 as nom_u32},
+    combinator::{map, value},
+    multi::separated_list1,
+    sequence::tuple,
+    IResult,
+};
+use std::{collections::BTreeMap, fs};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_7.txt")?;
+
+    {
+        let mut games_without_jokers = CardGame::parser(false)(&input).unwrap().1;
+        games_without_jokers.sort();
+        dbg!(games_without_jokers.calculate_winnings());
+    }
+
+    {
+        let mut games_with_jokers = CardGame::parser(true)(&input).unwrap().1;
+        games_with_jokers.sort();
+        dbg!(games_with_jokers.calculate_winnings());
+    }
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct CardGame(Vec<CardHand>);
+
+#[derive(Debug, PartialEq, Eq)]
+struct CardHand {
+    cards: [Card; 5],
+    bid: u32,
+}
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
+struct Card(u8);
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+enum CardRank {
+    HighCard,
+    OnePair,
+    TwoPair,
+    ThreeOfAKind,
+    FullHouse,
+    FourOfAKind,
+    FiveOfAKind,
+}
+
+impl CardGame {
+    fn parser(with_jokers: bool) -> impl FnMut(&str) -> IResult<&str, Self> {
+        move |input: &str| {
+            map(
+                separated_list1(line_ending, CardHand::parser(with_jokers)),
+                CardGame,
+            )(input)
+        }
+    }
+
+    fn sort(&mut self) {
+        self.0.sort()
+    }
+
+    fn calculate_winnings(&self) -> u32 {
+        self.0
+            .iter()
+            .enumerate()
+            .map(|(i, hand)| hand.bid * (i as u32 + 1))
+            .sum()
+    }
+}
+
+impl CardHand {
+    fn parser(with_jokers: bool) -> impl FnMut(&str) -> IResult<&str, Self> {
+        move |input: &str| {
+            map(
+                tuple((
+                    Card::parser(with_jokers),
+                    Card::parser(with_jokers),
+                    Card::parser(with_jokers),
+                    Card::parser(with_jokers),
+                    Card::parser(with_jokers),
+                    space1,
+                    nom_u32,
+                )),
+                |(c1, c2, c3, c4, c5, _, bid)| CardHand {
+                    cards: [c1, c2, c3, c4, c5],
+                    bid,
+                },
+            )(input)
+        }
+    }
+
+    fn card_rank(&self) -> CardRank {
+        let mut cards_set: BTreeMap<Card, u8> = BTreeMap::new();
+        for card in &self.cards {
+            *cards_set.entry(*card).or_insert(0) += 1;
+        }
+
+        let jokers = cards_set.get(&Card(1)).cloned().unwrap_or(0);
+        cards_set.remove(&Card(1));
+
+        let mut card_counts: Vec<u8> = cards_set.into_values().collect();
+        card_counts.sort_by(|a, b| b.cmp(a));
+
+        if card_counts.len() == 0 {
+            // all 5 were jokers!
+            CardRank::FiveOfAKind
+        } else {
+            card_counts[0] += jokers;
+            if card_counts[0] == 5 {
+                CardRank::FiveOfAKind
+            } else if card_counts[0] == 4 {
+                CardRank::FourOfAKind
+            } else if card_counts[0] == 3 && card_counts[1] == 2 {
+                CardRank::FullHouse
+            } else if card_counts[0] == 3 {
+                CardRank::ThreeOfAKind
+            } else if card_counts[0] == 2 && card_counts[1] == 2 {
+                CardRank::TwoPair
+            } else if card_counts[0] == 2 {
+                CardRank::OnePair
+            } else {
+                CardRank::HighCard
+            }
+        }
+    }
+}
+
+impl Card {
+    fn parser(with_jokers: bool) -> impl FnMut(&str) -> IResult<&str, Self> {
+        move |input: &str| {
+            map(
+                alt((
+                    value(2, nom_char('2')),
+                    value(3, nom_char('3')),
+                    value(4, nom_char('4')),
+                    value(5, nom_char('5')),
+                    value(6, nom_char('6')),
+                    value(7, nom_char('7')),
+                    value(8, nom_char('8')),
+                    value(9, nom_char('9')),
+                    value(10, nom_char('T')),
+                    value(if with_jokers { 1 } else { 11 }, nom_char('J')),
+                    value(12, nom_char('Q')),
+                    value(13, nom_char('K')),
+                    value(14, nom_char('A')),
+                )),
+                Card,
+            )(input)
+        }
+    }
+}
+
+impl std::cmp::Ord for CardHand {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.card_rank()
+            .cmp(&other.card_rank())
+            .then(self.cards.cmp(&other.cards))
+    }
+}
+
+impl std::cmp::PartialOrd for CardHand {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}