From abda4f84d88b7a7170b9e3cfa257a254cb6f5d88 Mon Sep 17 00:00:00 2001
From: George Thomas <georgefsthomas@gmail.com>
Date: Tue, 9 Dec 2025 19:17:25 +0000
Subject: [PATCH] Solve day 1 in Rust

---
 rust/main.rs         | 48 +++++++++++++++++++++++++++++-
 rust/puzzle.rs       |  5 ++++
 rust/puzzles/day1.rs | 70 ++++++++++++++++++++++++++++++++++++++++++++
 rust/puzzles/mod.rs  |  1 +
 4 files changed, 123 insertions(+), 1 deletion(-)
 create mode 100644 rust/puzzle.rs
 create mode 100644 rust/puzzles/day1.rs
 create mode 100644 rust/puzzles/mod.rs

diff --git a/rust/main.rs b/rust/main.rs
index e7a11a9..1b39588 100644
--- a/rust/main.rs
+++ b/rust/main.rs
@@ -1,3 +1,49 @@
+mod puzzle;
+mod puzzles;
+use crate::puzzle::Puzzle;
+use puzzles::day1;
+use std::fmt::Display;
+use std::fs;
+
+const PUZZLES: [&dyn SomePuzzle; 1] = [&day1::PUZZLE];
+
 fn main() {
-    println!("Hello, world!");
+    [false, true].iter().for_each(|is_real_data| {
+        let t = if *is_real_data { "real" } else { "examples" };
+        println!("{}", t);
+        PUZZLES.into_iter().for_each(|puzzle| {
+            println!("  {}", puzzle.number());
+            let input = fs::read_to_string(format!("../inputs/{}/{}", t, puzzle.number()))
+                .expect("no input file");
+            puzzle.run(&input).iter().zip(1..).for_each(|(output, n)| {
+                let expected =
+                    fs::read_to_string(format!("../outputs/{}/{}/{}", t, puzzle.number(), n))
+                        .expect("no golden file");
+                print!("    {}: ", n);
+                if expected == *output {
+                    println!("OK");
+                } else {
+                    println!(
+                        "expected {}, got {}",
+                        expected.trim_end(),
+                        output.trim_end()
+                    );
+                };
+            });
+        });
+    })
+}
+
+pub trait SomePuzzle {
+    fn number(&self) -> u32;
+    fn run(&self, input: &str) -> Vec<String>;
+}
+impl<Input, Output: Display, const N: usize> SomePuzzle for Puzzle<Input, Output, { N }> {
+    fn number(&self) -> u32 {
+        self.number
+    }
+    fn run(&self, s: &str) -> Vec<String> {
+        let input = (self.parser)(s);
+        self.parts.map(|p| p(&input).to_string() + "\n").to_vec()
+    }
 }
diff --git a/rust/puzzle.rs b/rust/puzzle.rs
new file mode 100644
index 0000000..8f212de
--- /dev/null
+++ b/rust/puzzle.rs
@@ -0,0 +1,5 @@
+pub struct Puzzle<Input, Output, const N: usize> {
+    pub number: u32,
+    pub parser: fn(&str) -> Input,
+    pub parts: [fn(&Input) -> Output; N],
+}
diff --git a/rust/puzzles/day1.rs b/rust/puzzles/day1.rs
new file mode 100644
index 0000000..dd04b67
--- /dev/null
+++ b/rust/puzzles/day1.rs
@@ -0,0 +1,70 @@
+use crate::puzzle::Puzzle;
+
+pub const PUZZLE: Puzzle<Vec<(Direction, i32)>, i32, 2> = Puzzle {
+    number: 1,
+    parser: |input| {
+        input
+            .lines()
+            .filter(|line| !line.is_empty())
+            .map(|line| {
+                let d = match line.chars().next().unwrap() {
+                    'L' => Direction::L,
+                    'R' => Direction::R,
+                    c => panic!("Unknown direction: {}", c),
+                };
+                let i: i32 = line[1..].parse().unwrap();
+                (d, i)
+            })
+            .collect()
+    },
+    parts: [
+        |instructions| {
+            let mut p = 50;
+            let mut r = 0;
+            for (d, i) in instructions {
+                let (_, p1) = step(*i, *d, p);
+                if p1 == 0 {
+                    r += 1;
+                }
+                p = p1;
+            }
+            r
+        },
+        |instructions| {
+            let mut p = 50;
+            let mut r = 0;
+            for (d, i) in instructions {
+                let (c, p1) = step(*i, *d, p);
+                let c1 = match d {
+                    Direction::R => c.abs(),
+                    Direction::L => {
+                        if p == 0 {
+                            c.abs() - 1
+                        } else if p1 == 0 {
+                            c.abs() + 1
+                        } else {
+                            c.abs()
+                        }
+                    }
+                };
+                r += c1;
+                p = p1;
+            }
+            r
+        },
+    ],
+};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Direction {
+    L,
+    R,
+}
+
+fn step(i: i32, d: Direction, p: i32) -> (i32, i32) {
+    let p1 = match d {
+        Direction::L => p - i,
+        Direction::R => p + i,
+    };
+    (p1.div_euclid(100), p1.rem_euclid(100))
+}
diff --git a/rust/puzzles/mod.rs b/rust/puzzles/mod.rs
new file mode 100644
index 0000000..ca9500f
--- /dev/null
+++ b/rust/puzzles/mod.rs
@@ -0,0 +1 @@
+pub(crate) mod day1;