day 2

d2/.gitignore

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+/target

d2/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "d2"
+version = "0.1.0"

d2/Cargo.toml

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+[package]
+name = "d2"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

d2/src/main.rs

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+use std::fs::read_to_string;
+use std::io::Error;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum RPS {
+    Rock,
+    Paper,
+    Scissor,
+}
+use RPS::*;
+
+impl RPS {
+    fn from_char(c: char) -> Self {
+        match c {
+            'A' | 'X' => Rock,
+            'B' | 'Y' => Paper,
+            'C' | 'Z' => Scissor,
+            _ => panic!()
+        }
+    }
+    pub fn score(self) -> u32 {
+        match self {
+            Rock => 1,
+            Paper => 2,
+            Scissor => 3,
+        }
+    }
+    pub fn outcome(opponent: Self, you: Self) -> Outcome {
+        match (you, opponent) {
+            (Rock, Rock) | (Paper, Paper) | (Scissor, Scissor) => Draw,
+            (Rock, Scissor) | (Paper, Rock) | (Scissor, Paper) => Win,
+            (Rock, Paper) | (Paper, Scissor) | (Scissor, Rock) => Loss,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Outcome {
+    Win,
+    Loss,
+    Draw,
+}
+use Outcome::*;
+
+impl Outcome {
+    pub fn from_char(c: char) -> Self {
+        match c {
+            'X' => Loss,
+            'Y' => Draw,
+            'Z' => Win,
+            _ => panic!()
+        }
+    }
+
+    pub fn score(self) -> u32 {
+        match self {
+            Win => 6,
+            Draw => 3,
+            Loss => 0
+        }
+    }
+
+    pub fn for_opponent(self, opponent: RPS) -> RPS {
+        match (self, opponent) {
+            (Win, Rock) | (Draw, Paper) | (Loss, Scissor) => Paper,
+            (Win, Paper) | (Draw, Scissor) | (Loss, Rock) => Scissor,
+            (Win, Scissor) | (Draw, Rock) | (Loss, Paper) => Rock,
+        }
+    }
+}
+
+fn main() -> Result<(), Error> {
+    let mut total_score_p1 = 0;
+    let mut total_score_p2 = 0;
+    for line in read_to_string("input.txt")?.split("\n") {
+        if line.is_empty() { continue }
+        let (opponent, you) = (line.chars().nth(0).unwrap(), line.chars().nth(2).unwrap());
+        let (opponent, your_move, outcome) = (RPS::from_char(opponent), RPS::from_char(you), Outcome::from_char(you));
+        let score_p1 = your_move.score() + RPS::outcome(opponent, your_move).score();
+        total_score_p1 += score_p1;
+        let score_p2 = outcome.score() + outcome.for_opponent(opponent).score();
+        total_score_p2 += score_p2;
+    }
+
+    println!("part 1: {}", total_score_p1);
+    println!("part 2: {}", total_score_p2);
+
+    Ok(())
+}