day 14

Author: spalberg

days/14/main.ts

@@ -0,0 +1,80 @@
+import { loadInput } from "utils";
+
+const defaultWidth = 101;
+const defaultHeight = 103;
+
+export function part1(
+  input: Array<string>,
+  width = defaultWidth,
+  height = defaultHeight,
+) {
+  const simulate100 = simulate(100, width, height);
+  const positions = input.map(parseInput).map(simulate100);
+  const halfWidth = Math.floor(width / 2);
+  const halfHeight = Math.floor(height / 2);
+  let q1 = 0, q2 = 0, q3 = 0, q4 = 0;
+  for (const { x, y } of positions) {
+    if (x < halfWidth && y < halfHeight) {
+      q1++;
+    } else if (x > halfWidth && y < halfHeight) {
+      q2++;
+    } else if (x < halfWidth && y > halfHeight) {
+      q3++;
+    } else if (x > halfWidth && y > halfHeight) {
+      q4++;
+    }
+  }
+  return q1 * q2 * q3 * q4;
+}
+
+export function part2(input: Array<string>) {
+  const robots = input.map(parseInput);
+  return simulateUntilUnique(robots, defaultWidth, defaultHeight);
+}
+
+type Robot = {
+  x: number;
+  y: number;
+  vx: number;
+  vy: number;
+};
+
+function simulate(seconds: number, width: number, height: number) {
+  return (robot: Robot) => {
+    const x = (((robot.x + robot.vx * seconds) % width) + width) % width;
+    const y = (((robot.y + robot.vy * seconds) % height) + height) % height;
+    return { x, y };
+  };
+}
+
+function simulateUntilUnique(
+  robots: Array<Robot>,
+  width: number,
+  height: number,
+) {
+  outer: for (let s = 1;; s++) {
+    const positions = new Set<string>();
+    const simulateS = simulate(s, width, height);
+    for (const robot of robots) {
+      const { x, y } = simulateS(robot);
+      const key = `${x},${y}`;
+      if (positions.has(key)) {
+        continue outer;
+      }
+      positions.add(key);
+    }
+    return s;
+  }
+}
+
+function parseInput(line: string): Robot {
+  const [l, r] = line.split(" v=");
+  const [x, y] = l.split("=")[1].split(",").map(Number);
+  const [vx, vy] = r.split(",").map(Number);
+  return { x, y, vx, vy };
+}
+
+if (import.meta.main) {
+  console.log(part1(await loadInput(14)));
+  console.log(part2(await loadInput(14)));
+}

days/14/main_test.ts

@@ -0,0 +1,35 @@
+import { expect } from "@std/expect";
+import { describe, it } from "@std/testing/bdd";
+import { part1, part2 } from "./main.ts";
+import { loadInput } from "utils";
+
+describe("day 14 example", () => {
+  const input = [
+    "p=0,4 v=3,-3",
+    "p=6,3 v=-1,-3",
+    "p=10,3 v=-1,2",
+    "p=2,0 v=2,-1",
+    "p=0,0 v=1,3",
+    "p=3,0 v=-2,-2",
+    "p=7,6 v=-1,-3",
+    "p=3,0 v=-1,-2",
+    "p=9,3 v=2,3",
+    "p=7,3 v=-1,2",
+    "p=2,4 v=2,-3",
+    "p=9,5 v=-3,-3",
+  ];
+
+  it("part 1", () => {
+    expect(part1(input, 11, 7)).toBe(12);
+  });
+});
+
+describe("day 14 solution", () => {
+  it("part 1", async () => {
+    expect(part1(await loadInput(14))).toBe(229839456);
+  });
+
+  it("part 2", async () => {
+    expect(part2(await loadInput(14))).toBe(7138);
+  });
+});

days/mod.ts

@@ -3,7 +3,7 @@ type Solution = { part1: PartFunction; part2: PartFunction };
 
 const days = new Map<number, Solution>();
 
-for (const day of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13]) {
+for (const day of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14]) {
   days.set(day, await import(`./${day}/main.ts`));
 }