mirror of
https://github.com/bertptrs/adventofcode.git
synced 2025-12-25 21:00:31 +01:00
110 lines
2.9 KiB
Rust
110 lines
2.9 KiB
Rust
use std::collections::VecDeque;
|
|
|
|
use anyhow::Context;
|
|
use anyhow::Result;
|
|
|
|
use crate::common::IndexSet;
|
|
|
|
fn can_travel(from: u8, to: u8) -> bool {
|
|
match (from, to) {
|
|
(b'S', b'a'..=b'b') => true,
|
|
(b'y'..=b'z', b'E') => true,
|
|
(b'a'..=b'z', b'a'..=b'z') => to <= from || to - from == 1,
|
|
_ => false,
|
|
}
|
|
}
|
|
|
|
fn parts_common(
|
|
input: &[u8],
|
|
starting_symbol: u8,
|
|
// Neither of these functions needs to be generic closures; function pointers would do as well.
|
|
// However, doing so causes the compiler not to inline them which in turn hurts performance by
|
|
// about 25%. I would have hoped the reduced code size would make up for it, but it seems that
|
|
// doesn't quite work for this particular benchmark.
|
|
is_end: impl Fn(u8) -> bool,
|
|
accessible: impl Fn(u8, u8) -> bool,
|
|
) -> Result<String> {
|
|
let width = input
|
|
.iter()
|
|
.position(|&c| c == b'\n')
|
|
.context("No newlines in input")?
|
|
+ 1;
|
|
|
|
let starting_pos = input
|
|
.iter()
|
|
.position(|&c| c == starting_symbol)
|
|
.context("Could not find starting position")?;
|
|
|
|
let mut visited = IndexSet::with_capacity(input.len());
|
|
|
|
let mut todo = VecDeque::new();
|
|
todo.push_back((0, starting_pos));
|
|
|
|
while let Some((dist, pos)) = todo.pop_front() {
|
|
// Implementing an early exit doesn't appear to be helpful; the additional branching appears
|
|
// to throw off the performance by 35%. Instead, we can simply wait for the destination to
|
|
// pop off of the todo queue.
|
|
//
|
|
// For reference, by the time we find the exit, the queue is roughly two dozen entries long,
|
|
// so the potential benefits of skipping it are minimal compared to the additional branching
|
|
// code involved.
|
|
if is_end(input[pos]) {
|
|
return Ok(dist.to_string());
|
|
}
|
|
|
|
let mut add_todo = |new: usize| {
|
|
if accessible(input[pos], input[new]) && visited.insert(new) {
|
|
todo.push_back((dist + 1, new));
|
|
}
|
|
};
|
|
|
|
if pos % width != 0 {
|
|
add_todo(pos - 1);
|
|
}
|
|
|
|
if pos % width != width - 1 {
|
|
add_todo(pos + 1)
|
|
}
|
|
|
|
if pos >= width {
|
|
add_todo(pos - width);
|
|
}
|
|
|
|
if pos + width < input.len() {
|
|
add_todo(pos + width);
|
|
}
|
|
}
|
|
|
|
anyhow::bail!("Did not find a valid route")
|
|
}
|
|
|
|
pub fn part1(input: &[u8]) -> Result<String> {
|
|
parts_common(input, b'S', |b| b == b'E', can_travel)
|
|
}
|
|
|
|
pub fn part2(input: &[u8]) -> Result<String> {
|
|
parts_common(
|
|
input,
|
|
b'E',
|
|
|b| b == b'a' || b == b'S',
|
|
|a, b| can_travel(b, a),
|
|
)
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
|
|
const SAMPLE: &[u8] = include_bytes!("samples/12.txt");
|
|
|
|
#[test]
|
|
fn sample_part1() {
|
|
assert_eq!(part1(SAMPLE).unwrap(), "31")
|
|
}
|
|
|
|
#[test]
|
|
fn sample_part2() {
|
|
assert_eq!(part2(SAMPLE).unwrap(), "29")
|
|
}
|
|
}
|