1 files changed, 109 insertions, 0 deletions
diff --git a/2023/src/bin/day_2.rs b/2023/src/bin/day_2.rs
new file mode 100644
index 0000000..6f19c1d
--- /dev/null
+++ b/2023/src/bin/day_2.rs
@@ -0,0 +1,109 @@
+use nom::{
+    bytes::complete::tag,
+    character::complete::{alpha1, line_ending, u32 as nom_u32},
+    combinator::map,
+    multi::separated_list1,
+    sequence::tuple,
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_2.txt")?;
+    let parsed = Games::parser(&input).unwrap().1;
+    let max_pull = Pull {
+        red: 12,
+        green: 13,
+        blue: 14,
+    };
+    dbg!(&parsed.valid_game_id_sum(&max_pull));
+    dbg!(&parsed.power_sum());
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct Games(Vec<Game>);
+
+#[derive(Debug)]
+struct Game {
+    id: u32,
+    pulls: Vec<Pull>,
+}
+
+#[derive(Debug, Default)]
+struct Pull {
+    red: u32,
+    green: u32,
+    blue: u32,
+}
+
+impl Games {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(separated_list1(line_ending, Game::parser), Games)(input)
+    }
+
+    fn valid_game_id_sum(&self, max_pull: &Pull) -> u32 {
+        self.0
+            .iter()
+            .filter(|game| game.is_valid(max_pull))
+            .map(|game| game.id)
+            .sum()
+    }
+
+    fn power_sum(&self) -> u32 {
+        self.0.iter().map(|game| game.min_pull().power()).sum()
+    }
+}
+
+impl Game {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(
+            tuple((
+                tag("Game "),
+                nom_u32,
+                tag(": "),
+                separated_list1(tag("; "), Pull::parser),
+            )),
+            |(_, id, _, pulls)| Game { id, pulls },
+        )(input)
+    }
+
+    fn is_valid(&self, max_pull: &Pull) -> bool {
+        self.pulls.iter().all(|pull| {
+            pull.red <= max_pull.red && pull.blue <= max_pull.blue && pull.green <= max_pull.green
+        })
+    }
+
+    fn min_pull(&self) -> Pull {
+        Pull {
+            red: self.pulls.iter().map(|p| p.red).max().unwrap_or(0),
+            blue: self.pulls.iter().map(|p| p.blue).max().unwrap_or(0),
+            green: self.pulls.iter().map(|p| p.green).max().unwrap_or(0),
+        }
+    }
+}
+
+impl Pull {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(
+            separated_list1(tag(", "), tuple((nom_u32, tag(" "), alpha1))),
+            |stones| {
+                let mut pull = Pull::default();
+                for (quantity, _, colour) in stones {
+                    match colour {
+                        "red" => pull.red += quantity,
+                        "blue" => pull.blue += quantity,
+                        "green" => pull.green += quantity,
+                        other => panic!("Unexpected colour, {}", other),
+                    };
+                }
+                pull
+            },
+        )(input)
+    }
+
+    fn power(&self) -> u32 {
+        self.red * self.blue * self.green
+    }
+}