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|
use anyhow::anyhow;
use std::{
env, fs,
ops::{Add, Sub},
str::FromStr,
};
#[derive(Debug, PartialEq, Eq)]
enum Rotation {
Left(u32),
Right(u32),
}
#[derive(Debug)]
struct ParseRotationError;
impl FromStr for Rotation {
type Err = ParseRotationError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let mut chars = s.chars();
let lr = chars.next().ok_or(ParseRotationError)?;
let n: u32 = chars
.collect::<String>()
.parse()
.map_err(|_| ParseRotationError)?;
match lr {
'L' => Ok(Self::Left(n)),
'R' => Ok(Self::Right(n)),
_ => Err(ParseRotationError),
}
}
}
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
struct Dial(u8);
struct RotateResult(u32, Dial);
impl Dial {
fn rotate(self, rot: &Rotation) -> RotateResult {
let pos = self.0 as u32;
match rot {
Rotation::Left(n) => {
if pos != 0 && *n >= pos {
let quot = n.div_ceil(100);
RotateResult(quot, self - *n)
} else {
RotateResult(0, self - *n)
}
}
Rotation::Right(n) => {
if n + pos >= 100 {
let quot = n.div_ceil(100);
RotateResult(quot, self + *n)
} else {
RotateResult(0, self + *n)
}
}
}
}
}
impl From<u8> for Dial {
fn from(value: u8) -> Self {
Self(value)
}
}
impl Add<u32> for Dial {
type Output = Self;
fn add(self, rhs: u32) -> Self::Output {
let n = self.0 as u32;
let m = (n + rhs) % 100;
Self(m as u8)
}
}
impl Sub<u32> for Dial {
type Output = Self;
fn sub(self, rhs: u32) -> Self::Output {
let n = self.0 as u32;
let m = (n + 100 - rhs % 100) % 100;
Self(m as u8)
}
}
impl PartialEq<u8> for Dial {
fn eq(&self, other: &u8) -> bool {
self.0 == *other
}
}
fn main() -> anyhow::Result<()> {
let mut args = env::args();
let input_path = args.nth(1).ok_or_else(|| anyhow!("usage: day1 INPUT"))?;
let input = fs::read_to_string(input_path)?;
let rotations: Vec<Rotation> = input
.split_whitespace()
.map(|s| s.parse().map_err(|_| anyhow!("bad rotation: {}", s)))
.collect::<anyhow::Result<_>>()?;
let mut dial = Dial::from(50);
let mut exact_zeros = 0;
let mut total_zeros = 0;
for rot in &rotations {
let RotateResult(zeros, new_dial) = dial.rotate(rot);
if new_dial == 0 {
exact_zeros += 1;
}
total_zeros += zeros;
dial = new_dial;
}
println!("Password: {}", exact_zeros);
println!("Password (method 0x434C49434B): {}", total_zeros);
Ok(())
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn parse_rotation() {
assert!("L2"
.parse::<Rotation>()
.is_ok_and(|rot| rot == Rotation::Left(2)));
assert!("R929"
.parse::<Rotation>()
.is_ok_and(|rot| rot == Rotation::Right(929)));
assert!("M1".parse::<Rotation>().is_err());
assert!("L".parse::<Rotation>().is_err());
assert!("2".parse::<Rotation>().is_err());
}
#[test]
fn dial_ops() {
let dial = Dial::from(50);
assert_eq!(dial + 1, 51);
assert_eq!(dial + 50, 0);
assert_eq!(dial + 100, 50);
assert_eq!(dial + 150, 0);
assert_eq!(dial + 2 + 48, 0);
assert_eq!(dial + 45 + 60, 55);
assert_eq!(dial - 45, 5);
assert_eq!(dial - 45 - 10, 95);
assert_eq!(dial - 1, 49);
assert_eq!(dial - 68, 82);
assert_eq!(dial - 68 - 30, 52);
assert_eq!(dial - 100, 50);
assert_eq!(dial - 998, 52);
assert_eq!(dial - 150, 0);
assert_eq!(dial - 51, 99);
assert_eq!(dial - 50, 0);
}
#[test]
fn dial_rotate() {
let mut dial = Dial::from(50);
let rotations = vec![
// Example data
(Rotation::Left(68), 1, 82),
(Rotation::Left(30), 0, 52),
(Rotation::Right(48), 1, 0),
(Rotation::Left(5), 0, 95),
(Rotation::Right(60), 1, 55),
(Rotation::Left(55), 1, 0),
(Rotation::Left(1), 0, 99),
(Rotation::Left(99), 1, 0),
(Rotation::Right(14), 0, 14),
(Rotation::Left(82), 1, 32),
// Additional data
(Rotation::Left(200), 2, 32),
(Rotation::Right(200), 2, 32),
(Rotation::Left(30), 0, 2),
(Rotation::Left(10), 1, 92),
(Rotation::Right(10), 1, 2),
(Rotation::Left(110), 2, 92),
(Rotation::Right(210), 3, 2),
(Rotation::Right(48), 0, 50),
(Rotation::Right(1000), 10, 50),
(Rotation::Right(48), 0, 98),
(Rotation::Left(651), 6, 47),
];
for (rot, expected_zeros, expected_dial) in &rotations {
let RotateResult(zeros, new_dial) = dial.rotate(rot);
assert_eq!(&zeros, expected_zeros, "rotating with {:?}", rot);
assert_eq!(&new_dial, expected_dial, "rotating with {:?}", rot);
dial = new_dial;
}
}
}
|
