day-13 (#27)

days/13/main.ts

@@ -0,0 +1,43 @@
+import { loadInput } from "utils";
+
+export function part1(input: Array<string>) {
+  return solve(input);
+}
+
+export function part2(input: Array<string>) {
+  return solve(input, 100_000_000_000_00);
+}
+
+function solve(input: Array<string>, dp = 0) {
+  let total = 0;
+  for (const { xa, ya, xb, yb, xp, yp } of parseInput(input, dp)) {
+    const b = (xa * yp - xp * ya) / (xa * yb - xb * ya);
+    const a = (yp - b * yb) / ya;
+    if (!Number.isInteger(a) || !Number.isInteger(b)) {
+      continue;
+    }
+    total += 3 * a + b;
+  }
+  return total;
+}
+
+function* parseInput(input: Array<string>, dp: number) {
+  for (let i = 0; i < input.length; i += 4) {
+    const buttonA = input[i].match(/Button A: X\+(\d+), Y\+(\d+)/)!;
+    const buttonB = input[i + 1].match(/Button B: X\+(\d+), Y\+(\d+)/)!;
+    const prize = input[i + 2].match(/Prize: X=(\d+), Y=(\d+)/)!;
+    yield {
+      xa: parseInt(buttonA[1], 10),
+      ya: parseInt(buttonA[2], 10),
+      xb: parseInt(buttonB[1], 10),
+      yb: parseInt(buttonB[2], 10),
+      xp: parseInt(prize[1], 10) + dp,
+      yp: parseInt(prize[2], 10) + dp,
+    };
+  }
+}
+
+if (import.meta.main) {
+  console.log(part1(await loadInput(13)));
+  console.log(part2(await loadInput(13)));
+}

days/13/main_test.ts

@@ -0,0 +1,42 @@
+import { expect } from "@std/expect";
+import { describe, it } from "@std/testing/bdd";
+import { part1, part2 } from "./main.ts";
+import { loadInput } from "utils";
+
+describe("day 13 example", () => {
+  const input = [
+    "Button A: X+94, Y+34",
+    "Button B: X+22, Y+67",
+    "Prize: X=8400, Y=5400",
+    "",
+    "Button A: X+26, Y+66",
+    "Button B: X+67, Y+21",
+    "Prize: X=12748, Y=12176",
+    "",
+    "Button A: X+17, Y+86",
+    "Button B: X+84, Y+37",
+    "Prize: X=7870, Y=6450",
+    "",
+    "Button A: X+69, Y+23",
+    "Button B: X+27, Y+71",
+    "Prize: X=18641, Y=10279",
+  ];
+
+  it("part 1", () => {
+    expect(part1(input)).toBe(480);
+  });
+
+  it("part 2", () => {
+    expect(part2(input)).toBe(875318608908);
+  });
+});
+
+describe("day 13 solution", () => {
+  it("part 1", async () => {
+    expect(part1(await loadInput(13))).toBe(37680);
+  });
+
+  it("part 2", async () => {
+    expect(part2(await loadInput(13))).toBe(87550094242995);
+  });
+});

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]) {
+for (const day of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13]) {
   days.set(day, await import(`./${day}/main.ts`));
 }