Initial solution

.gitignore

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+/target
+.idea

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day02"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "day02"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/main.rs

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+use std::fmt::{Display, Formatter};
+use std::fs::File;
+use std::io;
+use std::io::BufRead;
+use std::path::Path;
+
+#[derive(Debug)]
+#[derive(PartialEq, Eq)]
+struct Choice(u32);
+
+const ROCK: Choice = Choice(1);
+const PAPER: Choice = Choice(2);
+const SCISSORS: Choice = Choice(3);
+
+const LOOSE: Choice = ROCK;
+const DRAW: Choice = PAPER;
+const WIN: Choice = SCISSORS;
+
+impl From<&str> for Choice {
+    fn from(str: &str) -> Self {
+        match str {
+            "A" | "X" => ROCK,
+            "B" | "Y" => PAPER,
+            "C" | "Z" => SCISSORS,
+            _ => panic!("Invalid value")
+        }
+    }
+}
+
+impl Display for Choice {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            &ROCK => f.write_str("Rock"),
+            &PAPER => f.write_str("Paper"),
+            &SCISSORS => f.write_str("Scissors"),
+            _ => f.write_str("UNKNOWN"),
+        }
+    }
+}
+
+
+fn main() {
+    let path = Path::new("input.txt");
+    let file = File::open(&path).expect("Could not find file");
+    let lines = io::BufReader::new(file).lines();
+    let mut score1 = 0;
+    let mut score2 = 0;
+
+    for line in lines {
+        if let Ok(line) = line {
+            let v = line.split(' ').take(2).map(|str| Choice::from(str)).collect::<Vec<_>>();
+            let opponent = &v[0];
+            let me = &v[1];
+
+            // First challenge
+            let duel = match (opponent, me) {
+                (&ROCK, &ROCK) | (&PAPER, &PAPER) | (&SCISSORS, &SCISSORS) => 3,
+                (&SCISSORS, &ROCK) | (&PAPER, &SCISSORS) | (&ROCK, &PAPER) => 6,
+                _ => 0,
+            };
+            //println!("{} me {} opponent {} -> duel {}", score, me, opponent, duel);
+            score1 += duel + me.0;
+
+            // second challenge
+            score2 += match (opponent, me) {
+                (&ROCK, &LOOSE) => SCISSORS.0,
+                (&PAPER, &LOOSE) => ROCK.0,
+                (&SCISSORS, &LOOSE) => PAPER.0,
+                (hand, &DRAW) => 3 + hand.0,
+                (&ROCK, &WIN) => 6 + PAPER.0,
+                (&PAPER, &WIN) => 6 + SCISSORS.0,
+                (&SCISSORS, &WIN) => 6 + ROCK.0,
+                _ => 0, // Will never happen, but rustc can't know it
+            };
+        } else {
+            println!("Failed to parse : `{:?}`", line);
+        }
+    }
+
+    println!("first answer {}", score1);
+    println!("second answer {}", score2);
+}