2025: day01

Cargo.lock

@@ -133,6 +133,14 @@ dependencies = [
  "criterion 0.4.0",
 ]
 
+[[package]]
+name = "aoc2025"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "aoc",
+]
+
 [[package]]
 name = "atty"
 version = "0.2.14"

Cargo.toml

@@ -1,7 +1,7 @@
 [workspace]
 members = ["aoc20*", "aoc20*/aoc20*_bench"]
 
-default-members = ["aoc2023"]
+default-members = ["aoc2025"]
 
 resolver = "2"
 

aoc2025/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "aoc2025"
+version = "0.1.0"
+authors = ["Antoine Martin <antoine@alarsyo.net>"]
+edition = "2024"
+
+[dependencies]
+aoc = { path = "../aoc" }
+anyhow = "1.0"
+
+[lib]
+path = "src/lib.rs"
+
+[[bin]]
+name = "aoc2025"
+path = "src/main.rs"

aoc2025/input/day01_provided.txt

@@ -0,0 +1,10 @@
+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82

aoc2025/src/day01.rs

@@ -0,0 +1,135 @@
+use std::{fmt::Write, str::FromStr};
+
+use anyhow::{bail, Result};
+
+const INPUT: &str = include_str!("../input/day01.txt");
+const DIAL_SIZE: u16 = 100;
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+    writeln!(res, "part 2: {}", part2(INPUT)?)?;
+    Ok(res)
+}
+
+enum Rotation {
+    Left(u16),
+    Right(u16),
+}
+
+impl FromStr for Rotation {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        let dir = &s[..1];
+        let num = s[1..].parse()?;
+
+        match dir {
+            "L" => Ok(Rotation::Left(num)),
+            "R" => Ok(Rotation::Right(num)),
+            _ => bail!("rotation can only be left or right, got `{}'", dir),
+        }
+    }
+}
+
+impl Rotation {
+    fn apply(&self, state: u16) -> u16 {
+        match self {
+            Rotation::Left(num) => {
+                let num = num % DIAL_SIZE;
+                if num > state {
+                    DIAL_SIZE - (num - state)
+                } else {
+                    state - num
+                }
+            }
+            Rotation::Right(num) => (state + num) % DIAL_SIZE,
+        }
+    }
+
+    /// Counts the number of zeroes encountered while rotating the dial. Does NOT take the initial
+    /// state into account if it is 0.
+    fn apply_and_count_zeroes(&self, state: u16) -> (u16, usize) {
+        match self {
+            Rotation::Left(num) => {
+                let zeroes = (num / DIAL_SIZE) as usize;
+                let num = num % DIAL_SIZE;
+                if num > state {
+                    (
+                        DIAL_SIZE - (num - state),
+                        zeroes + if state != 0 { 1 } else { 0 },
+                    )
+                } else {
+                    let new_state = state - num;
+                    (new_state, zeroes + if new_state == 0 { 1 } else { 0 })
+                }
+            }
+            Rotation::Right(num) => (
+                (state + num) % DIAL_SIZE,
+                ((state + num) / DIAL_SIZE) as usize,
+            ),
+        }
+    }
+}
+
+fn part1(input: &str) -> Result<usize> {
+    let rotations = input
+        .lines()
+        .map(Rotation::from_str)
+        .collect::<Result<Vec<Rotation>>>()?;
+
+    let res = rotations
+        .iter()
+        .fold((50, 0), |(state, mut count), rot| {
+            let new_state = rot.apply(state);
+            if new_state == 0 {
+                count += 1;
+            }
+            (new_state, count)
+        })
+        .1;
+    Ok(res)
+}
+
+fn part2(input: &str) -> Result<usize> {
+    let rotations = input
+        .lines()
+        .map(Rotation::from_str)
+        .collect::<Result<Vec<Rotation>>>()?;
+
+    let res = rotations
+        .iter()
+        .fold((50, 0), |(state, count), rot| {
+            let (new_state, zeroes) = rot.apply_and_count_zeroes(state);
+            (new_state, count + zeroes)
+        })
+        .1;
+    Ok(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED: &str = include_str!("../input/day01_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 3);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 1092);
+    }
+
+    #[test]
+    fn part2_provided() {
+        assert_eq!(part2(PROVIDED).unwrap(), 6);
+    }
+
+    #[test]
+    fn part2_real() {
+        assert_eq!(part2(INPUT).unwrap(), 6616);
+    }
+}

aoc2025/src/lib.rs

@@ -0,0 +1 @@
+pub mod day01;

aoc2025/src/main.rs

@@ -0,0 +1,11 @@
+use anyhow::Result;
+
+use aoc::DayFunc;
+
+use aoc2025::day01;
+
+fn main() -> Result<()> {
+    let days: &[DayFunc] = &[day01::run];
+
+    aoc::run(days)
+}