Part One complete

index.ts

@@ -1,3 +1,3 @@
-import {runDaySeven} from "./src/day_seven";
+import {runDayEight} from "./src/day_eight";
 
-runDaySeven();
+runDayEight();

src/day_eight.test.ts

@@ -0,0 +1,29 @@
+import {DesertMap} from "./day_eight";
+
+describe('Day Eight', () => {
+	const input = `RL
+
+AAA = (BBB, CCC)
+BBB = (DDD, EEE)
+CCC = (ZZZ, GGG)
+DDD = (DDD, DDD)
+EEE = (EEE, EEE)
+GGG = (GGG, GGG)
+ZZZ = (ZZZ, ZZZ)`;
+
+	const repeatedInput = `LLR
+
+AAA = (BBB, BBB)
+BBB = (AAA, ZZZ)
+ZZZ = (ZZZ, ZZZ)`
+
+	it('should calculate the number of steps needed to reach ZZZ', () => {
+		const map = new DesertMap(input);
+		expect(map.stepsTo('ZZZ')).toEqual(2);
+	});
+
+	it('should repeat the pattern', () => {
+		const map = new DesertMap(repeatedInput);
+		expect(map.stepsTo('ZZZ')).toEqual(6);
+	})
+});

src/day_eight.ts

@@ -0,0 +1,66 @@
+import {anyCharOf, newline, uniLetter, whitespace} from "parjs";
+import {between, exactly, manySepBy, manyTill, stringify, then} from "parjs/combinators";
+import fs from "fs";
+
+const patternParser = anyCharOf("LR").pipe(manyTill(newline().pipe(exactly(2))));
+
+const nodeNameParser = uniLetter().pipe(exactly(3), stringify());
+const childParser = nodeNameParser.pipe(manySepBy(", "), exactly(2), between("(", ")"));
+const nodeParser = nodeNameParser.pipe(then(childParser.pipe(between(" = ", whitespace()))))
+
+const parser = patternParser.pipe(then(nodeParser.pipe(manySepBy(whitespace()))));
+
+type Maybe<T> = T | undefined;
+
+type Instruction = "L" | "R";
+type NodeName = string;
+type NodeChildren = [Maybe<NodeName>, Maybe<NodeName>];
+
+export class DesertMap {
+	private readonly pattern: Instruction[];
+
+	private map: Record<NodeName, NodeChildren> = {};
+
+	constructor(input: string) {
+		const [pattern, nodes] = parser.parse(input).value;
+
+		this.pattern = pattern as Instruction[];
+
+		for (const [name, [[leftNode, rightNode]]] of nodes) {
+			if (!this.map[name]) {
+				this.map[name] = [undefined, undefined];
+			}
+			const children = [leftNode !== name ? leftNode : undefined, rightNode !== name ? rightNode : undefined];
+			this.map[name] = children as NodeChildren;
+		}
+	}
+
+	public stepsTo(node: string): number {
+		let step = 0;
+		let curr = "AAA";
+
+		while (curr !== node) {
+			const instruction = this.pattern[step % this.pattern.length];
+
+			const [left, right] = this.map[curr];
+
+			if (instruction === "L" && left) {
+				curr = left;
+			} else if (instruction === "R" && right) {
+				curr = right;
+			}
+
+			if (!curr) return 0;
+
+			step++;
+		}
+		return step;
+	}
+}
+
+export const runDayEight = () => {
+	const input = fs.readFileSync('./inputs/day_eight_input.txt', 'utf-8').trimEnd();
+
+	const map = new DesertMap(input);
+	console.log(map.stepsTo('ZZZ'));
+}