105 lines
2.1 KiB
Rust
105 lines
2.1 KiB
Rust
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#![forbid(elided_lifetimes_in_paths, unsafe_code)]
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use aoc23::read;
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use chumsky::prelude::*;
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use std::collections::HashMap;
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enum Instruction {
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Left,
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Right
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}
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impl Instruction {
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fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
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choice((
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just('L').map(|_| Self::Left),
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just('R').map(|_| Self::Right)
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))
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}
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}
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#[derive(Debug)]
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struct Node {
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left: String,
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right: String
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}
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fn parse_node_name() -> impl Parser<char, String, Error = Simple<char>> {
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none_of([',', ')', ' '])
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.repeated()
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.at_least(1)
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.map(|chars| chars.into_iter().collect())
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}
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impl Node {
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fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
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just("(")
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.ignore_then(parse_node_name())
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.then_ignore(just(", "))
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.then(parse_node_name())
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.then_ignore(just(")"))
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.map(|(left, right)| Self { left, right })
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}
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}
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#[derive(Debug)]
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struct Network {
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nodes: HashMap<String, Node>
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}
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impl Network {
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fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
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parse_node_name()
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.then_ignore(just(" = "))
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.then(Node::parser())
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.then_ignore(just("\n"))
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.repeated()
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.map(|nodes| Self {
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nodes: nodes.into_iter().collect()
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})
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}
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fn node(&self, node: &str) -> &Node {
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self.nodes
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.get(node)
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.unwrap_or_else(|| panic!("Failed to get node {node:?}"))
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}
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fn left(&self, node: &str) -> &str {
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&self.node(node).left
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}
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fn right(&self, node: &str) -> &str {
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&self.node(node).right
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}
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}
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fn parser() -> impl Parser<char, (Vec<Instruction>, Network), Error = Simple<char>> {
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Instruction::parser()
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.repeated()
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.at_least(1)
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.then_ignore(just("\n\n"))
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.then(Network::parser())
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.then_ignore(end())
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}
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fn main() -> anyhow::Result<()> {
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let (instructions, network) = read("inputs/day8.txt", parser())?;
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// eprintln!("{network:?}");
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let mut curr_node = "AAA";
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let mut i = 0;
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let mut steps = 0;
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while curr_node != "ZZZ" {
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curr_node = match instructions[i] {
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Instruction::Left => network.left(curr_node),
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Instruction::Right => network.right(curr_node)
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};
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i = (i + 1) % instructions.len();
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steps += 1;
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}
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println!("{steps}");
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Ok(())
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}
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