day(02): refactor

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

src/bin/day02.rs

@@ -3,11 +3,12 @@ use std::str::FromStr;
 use aoc_2022::*;
 
 use color_eyre::eyre::Result;
+use itertools::Itertools;
 use thiserror::Error;
 use tracing::*;
 use tracing_subscriber::EnvFilter;
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum Shape {
     Rock,
     Paper,
@@ -28,7 +29,7 @@ impl Shape {
 enum ShapeError {
     #[error("empty string given")]
     Empty,
-    
+
     #[error("unknown shape ‹{0}›")]
     UnknownShape(String),
 }
@@ -85,20 +86,53 @@ impl FromStr for Round {
     }
 }
 
+fn find_strategy<P>(predicate: P) -> (usize, (Shape, Shape))
+where
+    P: FnMut(&(usize, (Shape, Shape))) -> bool,
+{
+    //   R P S
+    // R 3 0 6
+    // P 6 3 0
+    // S 0 6 3
+    vec![
+        // Loss
+        (Shape::Rock, Shape::Paper),
+        (Shape::Paper, Shape::Scissors),
+        (Shape::Scissors, Shape::Rock),
+        // Draw
+        (Shape::Rock, Shape::Rock),
+        (Shape::Paper, Shape::Paper),
+        (Shape::Scissors, Shape::Scissors),
+        // Win
+        (Shape::Rock, Shape::Scissors),
+        (Shape::Paper, Shape::Rock),
+        (Shape::Scissors, Shape::Paper),
+    ]
+    .into_iter()
+    .enumerate()
+    .find_or_first(predicate)
+    .unwrap()
+}
+
+fn find_result(strategy: &(Shape, Shape)) -> i32 {
+    3 * (find_strategy(|&(_, st)| st == *strategy).0 as i32 / 3)
+}
+
+fn find_result_for_outcome(opponent: Shape, outcome: Outcome) -> i32 {
+    let range = match outcome {
+        Outcome::Lose => 0..3,
+        Outcome::Draw => 3..6,
+        Outcome::Win => 6..9,
+    };
+    let (i, (shape, _)) = find_strategy(|&(i, (_, op))| range.contains(&i) && op == opponent);
+
+    3 * (i as i32 / 3) + shape.score()
+}
+
 impl Round {
     fn score(&self) -> i32 {
         let shape_score = self.me.score();
-
+        let result_score = find_result(&(self.me, self.opponent));
-        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
     }
 
@@ -111,23 +145,7 @@ impl Round {
     }
 
     fn expected_score(&self) -> i32 {
-        let result_score = match self.expected_outcome() {
+        find_result_for_outcome(self.opponent, 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
     }
 }