feat: 2019 Day 12

Author: mfulton26

2019/day/12/part/1/solve.test.ts

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+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("first example", () => {
+  const input = `\
+<x=-1, y=0, z=2>
+<x=2, y=-10, z=-7>
+<x=4, y=-8, z=8>
+<x=3, y=5, z=-1>`;
+
+  assertEquals(solve(input, { steps: 10 }), 179);
+});
+
+Deno.test("second example", () => {
+  const input = `\
+<x=-8, y=-10, z=0>
+<x=5, y=5, z=10>
+<x=2, y=-7, z=3>
+<x=9, y=-8, z=-3>`;
+
+  assertEquals(solve(input, { steps: 100 }), 1940);
+});

2019/day/12/part/1/solve.ts

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+import { parsePositions } from "../../positions.ts";
+
+export default function solve(input: string, { steps = 1_000 } = {}): number {
+  const moons = parsePositions(input).map((position) => {
+    const velocity = [0, 0, 0];
+    return { position, velocity };
+  });
+  for (let step = 0; step < steps; step++) {
+    for (let i = 0; i < moons.length; i++) {
+      for (let j = i + 1; j < moons.length; j++) {
+        for (let k = 0; k < 3; k++) {
+          const change = Math.sign(moons[j].position[k] - moons[i].position[k]);
+          moons[i].velocity[k] += change;
+          moons[j].velocity[k] -= change;
+        }
+      }
+    }
+    for (let i = 0; i < moons.length; i++) {
+      for (let k = 0; k < 3; k++) {
+        moons[i].position[k] += moons[i].velocity[k];
+      }
+    }
+  }
+  return moons.reduce((total, { position, velocity }) => {
+    const potential = position.reduce((sum, p) => sum + Math.abs(p), 0);
+    const kinetic = velocity.reduce((sum, v) => sum + Math.abs(v), 0);
+    return total + potential * kinetic;
+  }, 0);
+}

2019/day/12/part/2/solve.test.ts

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+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("first example", () => {
+  const input = `\
+<x=-1, y=0, z=2>
+<x=2, y=-10, z=-7>
+<x=4, y=-8, z=8>
+<x=3, y=5, z=-1>`;
+
+  assertEquals(solve(input), 2772);
+});
+
+Deno.test("second example", () => {
+  const input = `\
+<x=-8, y=-10, z=0>
+<x=5, y=5, z=10>
+<x=2, y=-7, z=3>
+<x=9, y=-8, z=-3>`;
+
+  assertEquals(solve(input), 4686774924);
+});

2019/day/12/part/2/solve.ts

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+import lcm from "@lib/lcm.ts";
+import { parsePositions } from "../../positions.ts";
+
+export default function solve(input: string) {
+  const moons = parsePositions(input).map((initialPosition) => {
+    const initialVelocity = [0, 0, 0];
+    const position = [...initialPosition], velocity = [...initialVelocity];
+    return ({ initialPosition, initialVelocity, position, velocity });
+  });
+  const repeats = [0, 0, 0];
+  for (let step = 0; repeats.some((r) => !r); step++) {
+    for (let i = 0; i < moons.length; i++) {
+      for (let j = i + 1; j < moons.length; j++) {
+        for (let k = 0; k < 3; k++) {
+          const change = Math.sign(moons[j].position[k] - moons[i].position[k]);
+          moons[i].velocity[k] += change;
+          moons[j].velocity[k] -= change;
+        }
+      }
+    }
+    for (let i = 0; i < moons.length; i++) {
+      for (let k = 0; k < 3; k++) {
+        moons[i].position[k] += moons[i].velocity[k];
+      }
+    }
+    for (let k = 0; k < repeats.length; k++) {
+      if (repeats[k]) continue;
+      const aligns = moons.every((moon) =>
+        moon.position[k] === moon.initialPosition[k] &&
+        moon.velocity[k] === moon.initialVelocity[k]
+      );
+      if (aligns) repeats[k] = step + 1;
+    }
+  }
+  return repeats.reduce(lcm);
+}

2019/day/12/positions.ts

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+export function parsePositions(input: string) {
+  return input.matchAll(/<x=(-?\d+), y=(-?\d+), z=(-?\d+)>/g)
+    .map(([, ...values]) => values.map(Number))
+    .toArray();
+}