1 files changed, 170 insertions, 0 deletions
diff --git a/src/day_02.rs b/src/day_02.rs
new file mode 100644
index 0000000..a27fbc8
--- /dev/null
+++ b/src/day_02.rs
@@ -0,0 +1,170 @@
+use std::str::FromStr;
+
+use anyhow::{anyhow, Result};
+
+use crate::{Problem, Solution};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct Game {
+    shapes: (Shape, Shape),
+    outcome: Outcome,
+    score: usize,
+}
+
+impl Game {
+    fn new(a: Shape, b: Shape, outcome: Outcome) -> Self {
+        Self {
+            shapes: (a, b),
+            outcome,
+            score: b as usize + outcome as usize,
+        }
+    }
+}
+
+impl From<(Shape, Shape)> for Game {
+    fn from((a, b): (Shape, Shape)) -> Self {
+        Self::new(a, b, (a, b).into())
+    }
+}
+
+impl From<(Shape, Outcome)> for Game {
+    fn from((a, outcome): (Shape, Outcome)) -> Self {
+        Self::new(a, (a, outcome).into(), outcome)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+enum Outcome {
+    Loss = 0,
+    Draw = 3,
+    Win = 6,
+}
+
+impl From<(Shape, Shape)> for Outcome {
+    fn from((a, b): (Shape, Shape)) -> Self {
+        match (a, b) {
+            (Shape::Rock, Shape::Rock) => Outcome::Draw,
+            (Shape::Rock, Shape::Paper) => Outcome::Win,
+            (Shape::Rock, Shape::Scissors) => Outcome::Loss,
+            (Shape::Paper, Shape::Rock) => Outcome::Loss,
+            (Shape::Paper, Shape::Paper) => Outcome::Draw,
+            (Shape::Paper, Shape::Scissors) => Outcome::Win,
+            (Shape::Scissors, Shape::Rock) => Outcome::Win,
+            (Shape::Scissors, Shape::Paper) => Outcome::Loss,
+            (Shape::Scissors, Shape::Scissors) => Outcome::Draw,
+        }
+    }
+}
+
+impl FromStr for Outcome {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "X" => Ok(Outcome::Loss),
+            "Y" => Ok(Outcome::Draw),
+            "Z" => Ok(Outcome::Win),
+            s => Err(anyhow!("Unknown symbol: {}", s)),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Shape {
+    Rock = 1,
+    Paper = 2,
+    Scissors = 3,
+}
+
+impl From<(Shape, Outcome)> for Shape {
+    fn from((shape, outcome): (Shape, Outcome)) -> Self {
+        match (shape, outcome) {
+            (Shape::Rock, Outcome::Draw) => Shape::Rock,
+            (Shape::Rock, Outcome::Win) => Shape::Paper,
+            (Shape::Rock, Outcome::Loss) => Shape::Scissors,
+            (Shape::Paper, Outcome::Loss) => Shape::Rock,
+            (Shape::Paper, Outcome::Draw) => Shape::Paper,
+            (Shape::Paper, Outcome::Win) => Shape::Scissors,
+            (Shape::Scissors, Outcome::Win) => Shape::Rock,
+            (Shape::Scissors, Outcome::Loss) => Shape::Paper,
+            (Shape::Scissors, Outcome::Draw) => Shape::Scissors,
+        }
+    }
+}
+
+impl FromStr for Shape {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "A" | "X" => Ok(Shape::Rock),
+            "B" | "Y" => Ok(Shape::Paper),
+            "C" | "Z" => Ok(Shape::Scissors),
+            s => Err(anyhow!("Unknown symbol: {}", s)),
+        }
+    }
+}
+
+pub struct Day02;
+
+impl Problem for Day02 {
+    const DAY: u8 = 3;
+
+    const INPUT: &'static str = include_str!("../input/day_2.txt");
+}
+
+impl Solution for Day02 {
+    type Answer1 = usize;
+
+    type Answer2 = usize;
+
+    fn part_1(input: &str) -> Result<Self::Answer1, anyhow::Error> {
+        input.lines().try_fold(0, |acc, l| {
+            let (a, b) = l
+                .split_once(' ')
+                .ok_or_else(|| anyhow!("Missing deliminator"))?;
+
+            let a: Shape = a.parse()?;
+            let b: Shape = b.parse()?;
+            let game: Game = (a, b).into();
+
+            Ok(acc + game.score)
+        })
+    }
+
+    fn part_2(input: &str) -> Result<Self::Answer2, anyhow::Error> {
+        input.lines().try_fold(0, |acc, l| {
+            let (a, outcome) = l
+                .split_once(' ')
+                .ok_or_else(|| anyhow!("Missing deliminator"))?;
+
+            let a: Shape = a.parse()?;
+            let outcome: Outcome = outcome.parse()?;
+            let game: Game = (a, outcome).into();
+
+            Ok(acc + game.score)
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = indoc::indoc! {"
+        A Y
+        B X
+        C Z
+    "};
+
+    #[test]
+    fn test_part_1_example() -> Result<()> {
+        Ok(assert_eq!(15, Day02::part_1(INPUT)?))
+    }
+
+    #[test]
+    fn test_part_2_example() -> Result<()> {
+        Ok(assert_eq!(12, Day02::part_2(INPUT)?))
+    }
+}