2024 day 12

2024/day-12/day12.ts

@@ -0,0 +1,162 @@
+import { sum } from "remeda";
+
+export function part1(input: string) {
+	let final = 0;
+
+	const startPoints: [number, number][] = [];
+	const lines = input.split("\n");
+	const grid = lines.map((l) => l.split(""));
+	for (let i = 0; i < lines.length; i++) {
+		const line = lines[i];
+		const letters = line.split("");
+		for (let j = 0; j < letters.length; j++) {
+			const letter = letters[j];
+			if (grid[i - 1]?.[j] !== letter && grid[i]?.[j - 1] !== letter) {
+				startPoints.push([i, j]);
+			}
+		}
+	}
+
+	while (startPoints.length > 0) {
+		const th = startPoints.pop();
+		const queue = [th];
+		const seen = new Set<string>();
+		while (queue.length > 0) {
+			const current = queue.shift();
+			if (!current) continue;
+			if (seen.has(current.join(","))) continue;
+			queue.push(
+				...getNeighbors(grid, current).map(
+					(x) => [x[0], x[1]] as [number, number],
+				),
+			);
+			seen.add(current.join(","));
+		}
+		const area = seen.size;
+
+		let perimiter = 0;
+		seen.values().forEach((x) => {
+			const [a, b] = x.split(",").map(Number);
+			const neighbors = getNeighbors(grid, [a, b]);
+			perimiter += 4 - neighbors.length;
+		});
+
+		final += perimiter * area;
+		seen.values().forEach((x) => {
+			const index = startPoints.findIndex((y) => y.join(",") === x);
+			if (index !== -1) {
+				startPoints.splice(index, 1);
+			}
+		});
+	}
+
+	return final;
+}
+
+export function part2(input: string) {
+	let final = 0;
+
+	const startPoints: [number, number][] = [];
+	const lines = input.split("\n");
+	const grid = lines.map((l) => l.split(""));
+	for (let i = 0; i < lines.length; i++) {
+		const line = lines[i];
+		const letters = line.split("");
+		for (let j = 0; j < letters.length; j++) {
+			const letter = letters[j];
+			if (grid[i - 1]?.[j] !== letter && grid[i]?.[j - 1] !== letter) {
+				startPoints.push([i, j]);
+			}
+		}
+	}
+
+	while (startPoints.length > 0) {
+		const th = startPoints.pop();
+		const queue = [th];
+		const seen = new Set<string>();
+		while (queue.length > 0) {
+			const current = queue.shift();
+			if (!current) continue;
+			if (seen.has(current.join(","))) continue;
+			queue.push(
+				...getNeighbors(grid, current).map(
+					(x) => [x[0], x[1]] as [number, number],
+				),
+			);
+			seen.add(current.join(","));
+		}
+
+		const area = seen.size;
+		const sides = getSides(seen);
+		final += sides * area;
+		seen.values().forEach((x) => {
+			const index = startPoints.findIndex((y) => y.join(",") === x);
+			if (index !== -1) {
+				startPoints.splice(index, 1);
+			}
+		});
+	}
+
+	return final;
+}
+
+function getSides(region: Set<string>) {
+	let sides = 0;
+	const cornerCandidates = new Set<string>();
+	for (const rc of region) {
+		const [r, c] = rc.split(",").map(Number);
+		for (const [cr, cc] of [
+			[r - 0.5, c - 0.5],
+			[r + 0.5, c - 0.5],
+			[r + 0.5, c + 0.5],
+			[r - 0.5, c + 0.5],
+		]) {
+			cornerCandidates.add([cr, cc].join(","));
+		}
+	}
+
+	for (const g of cornerCandidates.values().toArray().sort()) {
+		const [cr, cc] = g.split(",").map(Number);
+		const config = [];
+		for (const [sr, sc] of [
+			[cr - 0.5, cc - 0.5],
+			[cr + 0.5, cc - 0.5],
+			[cr + 0.5, cc + 0.5],
+			[cr - 0.5, cc + 0.5],
+		]) {
+			if (region.has([sr, sc].join(","))) {
+				config.push(1);
+			} else config.push(0);
+		}
+		const number = sum(config);
+		if (number === 3 || number === 1) {
+			sides++;
+		}
+		if (number === 2) {
+			if (
+				(config[0] === 0 && config[2] === 0) ||
+				(config[1] === 0 && config[3] === 0)
+			) {
+				sides += 2;
+			}
+		}
+	}
+	return sides;
+}
+
+function getNeighbors(
+	grid: string[][],
+	[x, y]: [number, number],
+): [number, number][] {
+	const currentLetter = grid[x][y];
+	const up = grid[x - 1]?.[y];
+	const down = grid[x + 1]?.[y];
+	const right = grid[x]?.[y + 1];
+	const left = grid[x]?.[y - 1];
+	return [
+		up === currentLetter && [x - 1, y],
+		down === currentLetter && [x + 1, y],
+		right === currentLetter && [x, y + 1],
+		left === currentLetter && [x, y - 1],
+	].filter(Boolean) as [number, number][];
+}