day(02): add initial solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

samples/day02.txt

@@ -0,0 +1,3 @@
+A Y
+B X
+C Z

src/bin/day02.rs

@@ -0,0 +1,156 @@
+use aoc_2022::*;
+
+use color_eyre::eyre::Result;
+use itertools::Itertools;
+use tracing::*;
+use tracing_subscriber::EnvFilter;
+
+#[derive(Debug, Clone, Copy)]
+enum Shape {
+    Rock,
+    Paper,
+    Scissors,
+}
+
+impl Shape {
+    fn score(&self) -> i32 {
+        match self {
+            Shape::Rock => 1,
+            Shape::Paper => 2,
+            Shape::Scissors => 3,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Outcome {
+    Lose,
+    Draw,
+    Win,
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Round {
+    opponent: Shape,
+    me: Shape,
+}
+
+impl Round {
+    fn score(&self) -> i32 {
+        let shape_score = self.me.score();
+
+        let result_score = match (self.me, self.opponent) {
+            (Shape::Scissors, Shape::Paper) => 6,
+            (Shape::Paper, Shape::Rock) => 6,
+            (Shape::Rock, Shape::Scissors) => 6,
+            (Shape::Paper, Shape::Scissors) => 0,
+            (Shape::Rock, Shape::Paper) => 0,
+            (Shape::Scissors, Shape::Rock) => 0,
+            _ => 3,
+        };
+
+        shape_score + result_score
+    }
+
+    fn expected_outcome(&self) -> Outcome {
+        match self.me {
+            Shape::Rock => Outcome::Lose,
+            Shape::Paper => Outcome::Draw,
+            Shape::Scissors => Outcome::Win,
+        }
+    }
+
+    fn expected_score(&self) -> i32 {
+        let result_score = match self.expected_outcome() {
+            Outcome::Lose => 0,
+            Outcome::Draw => 3,
+            Outcome::Win => 6,
+        };
+
+        let shape_score = match (self.expected_outcome(), self.opponent) {
+            (Outcome::Lose, Shape::Rock) => Shape::Scissors.score(),
+            (Outcome::Lose, Shape::Paper) => Shape::Rock.score(),
+            (Outcome::Lose, Shape::Scissors) => Shape::Paper.score(),
+            (Outcome::Win, Shape::Rock) => Shape::Paper.score(),
+            (Outcome::Win, Shape::Paper) => Shape::Scissors.score(),
+            (Outcome::Win, Shape::Scissors) => Shape::Rock.score(),
+            _ => self.opponent.score(),
+        };
+
+        result_score + shape_score
+    }
+}
+
+type Input = Vec<Round>;
+type Output = i32;
+
+fn part_1(input: &Input) -> Output {
+    input.iter().map(Round::score).sum()
+}
+
+fn part_2(input: &Input) -> Output {
+    input.iter().map(Round::expected_score).sum()
+}
+
+fn parse_input(pathname: &str) -> Input {
+    file_to_lines(pathname)
+        .iter()
+        .map(|s| {
+            let mut split_str = s.split(" ");
+
+            let opponent = split_str.next().unwrap();
+            let me = split_str.next().unwrap();
+
+            Round {
+                opponent: match opponent {
+                    "A" => Shape::Rock,
+                    "B" => Shape::Paper,
+                    "C" => Shape::Scissors,
+                    _ => panic!("invalid choice"),
+                },
+                me: match me {
+                    "X" => Shape::Rock,
+                    "Y" => Shape::Paper,
+                    "Z" => Shape::Scissors,
+                    _ => panic!("invalid choice"),
+                },
+            }
+        })
+        .collect()
+}
+
+fn main() -> Result<()> {
+    tracing_subscriber::fmt()
+        .with_env_filter(EnvFilter::from_default_env())
+        .with_target(false)
+        .with_file(true)
+        .with_line_number(true)
+        .without_time()
+        .compact()
+        .init();
+    color_eyre::install()?;
+
+    let input = parse_input("inputs/day02.txt");
+
+    info!("Part 1: {}", part_1(&input));
+    info!("Part 2: {}", part_2(&input));
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_1() {
+        let sample = parse_input("samples/day02.txt");
+        assert_eq!(part_1(&sample), 15);
+    }
+
+    #[test]
+    fn test_part_2() {
+        let sample = parse_input("samples/day02.txt");
+        assert_eq!(part_2(&sample), 12);
+    }
+}