Solution for day 12 (2019)

Author: joshthompson

2019/12/index.js

@@ -0,0 +1,63 @@
+const fs = require('fs')
+
+const coords = [0, 1, 2]
+const gcd = (a, b) => a ? gcd(b % a, a) : b
+const lcm = (a, b) => a * b / gcd(a, b)
+
+fs.readFile(`${__dirname}/input.txt`, (_e, data) => {
+	const moons = data.toString().split('\n').filter(v => v.length).map(makeMoon)
+	console.log('Part 1', part1(moons))
+	console.log('Part 2', part2(moons))
+})
+
+function part1(init) {
+	const moons = JSON.parse(JSON.stringify(init))
+	for (let i = 0; i < 1000; i++) {
+		coords.forEach(c => update(moons, c))
+	}
+	return systemEnergy(moons)
+}
+
+function part2(init) {
+	const moons = JSON.parse(JSON.stringify(init))
+	let results = [];
+	coords.forEach(c => {
+		for (let i = 0; true; i++) {
+			update(moons, c)
+			if (!moons.find((m, i) => m.pos[c] !== init[i].pos[c] || m.vel[c] !== 0)) {
+				return results[c] = i + 1
+			}
+		}
+	})
+	return results.reduce(lcm, 1)
+}
+
+function update(moons, c) {
+	moons.forEach(a => moons.forEach(b => {
+		if (a.pos[c] > b.pos[c]) a.vel[c]--
+		else if (a.pos[c] < b.pos[c]) a.vel[c]++
+	}))
+	moons.forEach(moon => moon.pos[c] += moon.vel[c])
+}
+
+function systemEnergy(moons) {
+	return moons.map(moonEnergy).reduce((a, b) => a + b, 0)
+}
+
+function moonEnergy(moon) {
+	const potential = moon.pos.reduce((a, b) => Math.abs(a) + Math.abs(b), 0)
+	const kinetic = moon.vel.reduce((a, b) => Math.abs(a) + Math.abs(b), 0)
+	return potential * kinetic
+}
+
+function makeMoon(str, i) {
+	return {
+		name: ['Io', 'Europa', 'Ganymede', 'Callisto'][i],
+		pos: [
+			parseInt(/x\=([-\d]*)/g.exec(str)[1]),
+			parseInt(/y\=([-\d]*)/g.exec(str)[1]),
+			parseInt(/z\=([-\d]*)/g.exec(str)[1])
+		],
+		vel: [0, 0, 0]
+	}
+}

2019/12/input.txt

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+<x=3, y=2, z=-6>
+<x=-13, y=18, z=10>
+<x=-8, y=-1, z=13>
+<x=5, y=10, z=4>