From b2dc39f54ae792887278642112c9fba3b839a452 Mon Sep 17 00:00:00 2001 From: Xiretza Date: Sat, 9 Dec 2023 11:26:25 +0000 Subject: [PATCH] 2023 day8/rust: add solution --- 2023/day8/rust/Cargo.toml | 12 +++ 2023/day8/rust/src/main.rs | 204 +++++++++++++++++++++++++++++++++++++ Cargo.lock | 10 ++ Cargo.toml | 1 + 4 files changed, 227 insertions(+) create mode 100644 2023/day8/rust/Cargo.toml create mode 100644 2023/day8/rust/src/main.rs diff --git a/2023/day8/rust/Cargo.toml b/2023/day8/rust/Cargo.toml new file mode 100644 index 0000000..39567bc --- /dev/null +++ b/2023/day8/rust/Cargo.toml @@ -0,0 +1,12 @@ +[package] +name = "rust_2023_08" +version = "0.1.0" +edition = "2021" + +# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html + +[dependencies] +aoc = { path = "../../../common/rust" } +either = "1.9.0" +itertools = "0.12.0" +petgraph = "0.6.4" diff --git a/2023/day8/rust/src/main.rs b/2023/day8/rust/src/main.rs new file mode 100644 index 0000000..9230759 --- /dev/null +++ b/2023/day8/rust/src/main.rs @@ -0,0 +1,204 @@ +#![warn(clippy::pedantic)] + +use std::{cmp::PartialEq, collections::HashMap, fmt::Debug, io::stdin, num::NonZeroUsize}; + +use either::Either; +use itertools::Itertools; +use petgraph::{ + prelude::DiGraphMap, + visit::{Data, EdgeRef, GraphBase, IntoEdgesDirected, Walker}, + Direction::Outgoing, +}; + +#[derive(Debug, Clone, Copy, PartialEq, Eq)] +enum Step { + Left, + Right, +} + +#[derive(Debug, Clone, Copy, PartialEq, Eq)] +enum Edge { + Left, + Right, + Both, +} + +impl Edge { + pub fn matches(self, s: Step) -> bool { + match (self, s) { + (Edge::Left, Step::Left) | (Edge::Right, Step::Right) | (Edge::Both, _) => true, + (Edge::Right, Step::Left) | (Edge::Left, Step::Right) => false, + } + } +} + +struct StepsWalker<'a> { + current_node: &'a str, + step_idx: usize, + steps: Vec, +} + +impl<'a> StepsWalker<'a> { + pub fn new(start: &'a str, steps: Vec) -> Self { + Self { + current_node: start, + steps, + step_idx: 0, + } + } + + /// Resets the step sequence to the beginning. + pub fn reset_steps(&mut self) { + self.step_idx = 0; + } + + /// Steps once. Returns `None` if all steps have been performed. + pub fn step(&mut self, context: G) -> Option<&'a str> + where + G: IntoEdgesDirected + GraphBase + Data, + { + let step = self.steps.get(self.step_idx)?; + let mut targets = context + .edges_directed(self.current_node, Outgoing) + .filter_map(|e| e.weight().matches(*step).then_some(e.target())); + let next_node = targets.next()?; + assert_eq!( + targets.next(), + None, + "More than one {:?} edge from {:?}", + step, + self.current_node + ); + + self.current_node = next_node; + self.step_idx += 1; + + Some(self.current_node) + } + + pub fn find_end_positions(mut self, context: G) -> impl Iterator + where + G: IntoEdgesDirected + GraphBase + Data, + { + let mut seen = HashMap::new(); + let mut pos = 1_usize; + loop { + while let Some(node) = self.step(context) { + let key = (node, self.step_idx - 1); + + if let Some(&loop_start) = seen.get(&key) { + let period = NonZeroUsize::new(pos - loop_start).unwrap(); + let mut ends: Vec<_> = seen + .into_iter() + .filter_map(|((node, _step_idx), pos)| node.ends_with('Z').then_some(pos)) + .collect(); + ends.sort_unstable(); + let (initial, repeating) = ends + .into_iter() + .partition::, _>(|&pos| pos < loop_start); + return initial.into_iter().chain((0_usize..).flat_map(move |n| { + repeating + .clone() + .into_iter() + .map(move |pos| pos + n * period.get()) + })); + } + + seen.insert(key, pos); + pos += 1; + } + self.reset_steps(); + } + } +} + +impl<'a, G> Walker for StepsWalker<'a> +where + G: IntoEdgesDirected + GraphBase + Data, +{ + type Item = &'a str; + + fn walk_next(&mut self, context: G) -> Option { + Some(if let Some(node) = self.step(context) { + node + } else { + self.reset_steps(); + self.step(context).unwrap() + }) + } +} + +fn main() { + let mut lines = stdin().lines().map(Result::unwrap); + + let steps: Vec<_> = lines + .next() + .unwrap() + .chars() + .map(|c| match c { + 'L' => Step::Left, + 'R' => Step::Right, + _ => unreachable!(), + }) + .collect(); + + let lines: Vec<_> = lines.skip(1).collect(); + + let graph: DiGraphMap<_, _> = lines + .iter() + .flat_map(|l| { + let (from, to) = l.split_once(" = ").unwrap(); + let (left, right) = to + .strip_prefix('(') + .unwrap() + .strip_suffix(')') + .unwrap() + .split_once(", ") + .unwrap(); + + if left == right { + Either::Left([(from, left, Edge::Both)]) + } else { + Either::Right([(from, left, Edge::Left), (from, right, Edge::Right)]) + } + .into_iter() + }) + .collect(); + + let walker = StepsWalker::new("AAA", steps.clone()); + + println!( + "{}", + walker.iter(&graph).position(|n| n == "ZZZ").unwrap() + 1 + ); + + let start_nodes = graph.nodes().filter(|n| n.ends_with('A')); + let mut end_positions: Vec<_> = start_nodes + .map(|start| { + StepsWalker::new(start, steps.clone()) + .find_end_positions(&graph) + .peekable() + }) + .collect(); + + let num_steps = loop { + let target = *end_positions[0].peek().unwrap(); + for positions in &mut end_positions { + positions + .peeking_take_while(|&pos| pos < target) + .for_each(|_| {}); + } + + if end_positions + .iter_mut() + .map(|positions| positions.peek()) + .all_equal() + { + break target; + } + + end_positions[0].next().unwrap(); + }; + + println!("{num_steps}"); +} diff --git a/Cargo.lock b/Cargo.lock index 03e1348..b08ecf3 100644 --- a/Cargo.lock +++ b/Cargo.lock @@ -669,6 +669,16 @@ dependencies = [ "strum 0.25.0", ] +[[package]] +name = "rust_2023_08" +version = "0.1.0" +dependencies = [ + "aoc", + "either", + "itertools 0.12.0", + "petgraph", +] + [[package]] name = "rustversion" version = "1.0.14" diff --git a/Cargo.toml b/Cargo.toml index 1e30df2..96c1b7c 100644 --- a/Cargo.toml +++ b/Cargo.toml @@ -33,4 +33,5 @@ members = [ "2023/day5/rust", "2023/day6/rust", "2023/day7/rust", + "2023/day8/rust", ]