day 8 part 1

src/bin/day8.rs

@@ -0,0 +1,104 @@
+#![forbid(elided_lifetimes_in_paths, unsafe_code)]
+
+use aoc23::read;
+use chumsky::prelude::*;
+use std::collections::HashMap;
+
+enum Instruction {
+	Left,
+	Right
+}
+
+impl Instruction {
+	fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
+		choice((
+			just('L').map(|_| Self::Left),
+			just('R').map(|_| Self::Right)
+		))
+	}
+}
+
+#[derive(Debug)]
+struct Node {
+	left: String,
+	right: String
+}
+
+fn parse_node_name() -> impl Parser<char, String, Error = Simple<char>> {
+	none_of([',', ')', ' '])
+		.repeated()
+		.at_least(1)
+		.map(|chars| chars.into_iter().collect())
+}
+
+impl Node {
+	fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
+		just("(")
+			.ignore_then(parse_node_name())
+			.then_ignore(just(", "))
+			.then(parse_node_name())
+			.then_ignore(just(")"))
+			.map(|(left, right)| Self { left, right })
+	}
+}
+
+#[derive(Debug)]
+struct Network {
+	nodes: HashMap<String, Node>
+}
+
+impl Network {
+	fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
+		parse_node_name()
+			.then_ignore(just(" = "))
+			.then(Node::parser())
+			.then_ignore(just("\n"))
+			.repeated()
+			.map(|nodes| Self {
+				nodes: nodes.into_iter().collect()
+			})
+	}
+
+	fn node(&self, node: &str) -> &Node {
+		self.nodes
+			.get(node)
+			.unwrap_or_else(|| panic!("Failed to get node {node:?}"))
+	}
+
+	fn left(&self, node: &str) -> &str {
+		&self.node(node).left
+	}
+
+	fn right(&self, node: &str) -> &str {
+		&self.node(node).right
+	}
+}
+
+fn parser() -> impl Parser<char, (Vec<Instruction>, Network), Error = Simple<char>> {
+	Instruction::parser()
+		.repeated()
+		.at_least(1)
+		.then_ignore(just("\n\n"))
+		.then(Network::parser())
+		.then_ignore(end())
+}
+
+fn main() -> anyhow::Result<()> {
+	let (instructions, network) = read("inputs/day8.txt", parser())?;
+	// eprintln!("{network:?}");
+
+	let mut curr_node = "AAA";
+	let mut i = 0;
+	let mut steps = 0;
+	while curr_node != "ZZZ" {
+		curr_node = match instructions[i] {
+			Instruction::Left => network.left(curr_node),
+			Instruction::Right => network.right(curr_node)
+		};
+		i = (i + 1) % instructions.len();
+		steps += 1;
+	}
+	println!("{steps}");
+
+	Ok(())
+}