2024 day 12

Author: FriendlyUser1

2024/day12/fences.js

@@ -0,0 +1,124 @@
+class Plot {
+	/** @type {number} */ x;
+	/** @type {number} */ y;
+	/** @type {string} */ value;
+	/** @type {Region} */ region;
+
+	constructor(x, y, value) {
+		this.x = x;
+		this.y = y;
+		this.value = value;
+		this.region = null;
+	}
+}
+
+class Region {
+	/** @type {Set<Plot>} plots */ plots;
+
+	constructor() {
+		this.area = 0;
+		this.perimeter = 0;
+		this.sides = 0;
+		this.plots = new Set();
+	}
+}
+
+const Farm = require("fs")
+		.readFileSync("./input.txt", "utf-8")
+		.split("\n")
+		.map((r, y) => r.split("").map((c, x) => new Plot(x, y, c))),
+	farmSize = Farm.length - 1;
+
+/** @type {Set<Region>} regions */
+const regions = new Set();
+
+// Processes all adjacent plots to define a region
+// Returns a list of adjacent plots from other regions
+function discoverRegion(/** @type {Plot} root */ root) {
+	const foreignPlots = new Set();
+
+	/** @type {Plot[]} plotQueue */
+	let plotQueue = [];
+
+	root.region = new Region();
+	regions.add(root.region);
+
+	plotQueue.push(root);
+
+	while (plotQueue.length > 0) {
+		const plot = plotQueue.shift();
+		plot.region.area++;
+		plot.region.plots.add(plot);
+
+		let adjacents = [];
+
+		const n = plot.y > 0 ? Farm[plot.y - 1][plot.x] : null;
+		const s = plot.y < farmSize ? Farm[plot.y + 1][plot.x] : null;
+		const w = plot.x > 0 ? Farm[plot.y][plot.x - 1] : null;
+		const e = plot.x < farmSize ? Farm[plot.y][plot.x + 1] : null;
+
+		adjacents.push(n, s, w, e);
+
+		for (let i = 0; i < adjacents.length; i++) {
+			if (!adjacents[i]) plot.region.perimeter++;
+			else {
+				if (adjacents[i].value !== plot.value) plot.region.perimeter++;
+				if (adjacents[i].region === null) {
+					if (adjacents[i].value === plot.value) {
+						adjacents[i].region = root.region;
+						plotQueue.push(adjacents[i]);
+					} else foreignPlots.add(adjacents[i]);
+				}
+			}
+		}
+	}
+
+	return [...foreignPlots];
+}
+
+let plotsToProcess = discoverRegion(Farm[0][0]);
+while (plotsToProcess.length > 0) {
+	const plotToProcess = plotsToProcess.shift();
+
+	if (plotToProcess.region === null)
+		plotsToProcess.push(...discoverRegion(plotToProcess));
+}
+
+for (const region of regions.values()) {
+	for (const plot of region.plots.values()) {
+		const dir = (x, y) =>
+			[...region.plots].filter((p) => p.x === x && p.y === y)[0];
+
+		let { x, y } = plot;
+		const n = dir(x, y - 1),
+			s = dir(x, y + 1),
+			w = dir(x - 1, y),
+			e = dir(x + 1, y),
+			ne = dir(x + 1, y - 1),
+			nw = dir(x - 1, y - 1),
+			sw = dir(x - 1, y + 1),
+			se = dir(x + 1, y + 1);
+
+		// Basic corners
+		if (!n && !w) region.sides++;
+		if (!n && !e) region.sides++;
+		if (!s && !w) region.sides++;
+		if (!s && !e) region.sides++;
+
+		// Inner corners
+		if (n && w && !nw) region.sides++;
+		if (n && e && !ne) region.sides++;
+		if (s && w && !sw) region.sides++;
+		if (s && e && !se) region.sides++;
+	}
+}
+
+console.log(
+	"Fence price:",
+	[...regions].reduce((acc, region) => acc + region.area * region.perimeter, 0)
+);
+
+console.log(
+	"Discounted price:",
+	[...regions].reduce((acc, region) => acc + region.area * region.sides, 0)
+);