Day 12

Author: ansf

Makefile

@@ -52,3 +52,8 @@ day11:
 	npx ts-node day11.ts
 day11-2:
 	npx ts-node day11-2.ts
+
+day12:
+	npx ts-node day12.ts
+day12-2:
+	npx ts-node day12-2.ts

day12-2.ts

@@ -0,0 +1,83 @@
+import * as fs from "fs"
+const abs = Math.abs
+
+const input = fs.readFileSync("input-day12.txt", "utf8")
+
+function parse(input: string): Vector[] {
+    const regEx = /\<x=(-?\d+), y=(-?\d+), z=(-?\d+)\>/g
+    let m: RegExpExecArray
+    const vs = []
+    while ((m = regEx.exec(input)) !== null) {
+        vs.push([m[1], m[2], m[3]].map(Number))
+    }
+    return vs
+}
+
+type Vector = [number, number, number]
+
+function add(v1: Vector, v2: Vector): Vector {
+    return [v1[0] + v2[0], v1[1] + v2[1], v1[2] + v2[2]]
+}
+function sub(v1: Vector, v2: Vector): Vector {
+    return [v1[0] - v2[0], v1[1] - v2[1], v1[2] - v2[2]]
+}
+function sign(v1: Vector): Vector {
+    return [v1[0], v1[1], v1[2]].map(Math.sign) as Vector
+}
+function gcd(a: number, b: number) {
+    if (a == 0) return abs(b)
+    if (b == 0) return abs(a)
+
+    let h: number
+    do {
+        h = a % b
+        a = b
+        b = h
+    } while (b != 0)
+    return abs(a)
+}
+function lcm(a: number, b: number) {
+    return abs(a * b) / gcd(a, b)
+}
+
+const initialPs = parse(input)
+const initialVs = initialPs.map(_ => <Vector>[0, 0, 0])
+
+function period(axis: number): number {
+    let ps = initialPs.slice()
+    let vs = initialVs.slice()
+
+    let s = 0
+    while (true) {
+        vs = gravity(ps, vs)
+        ps = move(ps, vs)
+
+        if (ps.every((p, i) => p[axis] === initialPs[i][axis] && vs[i][axis] === initialVs[i][axis])) {
+            console.log(`equality after step ${s + 1}`)
+            return s + 1
+        }
+        s++
+    }
+}
+
+const periods = [0, 1, 2].map(period)
+console.log(lcm(lcm(periods[2], periods[1]), periods[0]))
+
+
+function gravity(ps: Vector[], vs: Vector[]): Vector[] {
+    ps.forEach((p1, i) => {
+        ps.forEach((p2, j) => {
+            if (i == j) {
+                return
+            }
+
+            const v = vs[i]
+            vs[i] = add(v, sign(sub(p2, p1)))
+        })
+    })
+    return vs
+}
+
+function move(ps: Vector[], vs: Vector[]): Vector[] {
+    return ps.map((p, i) => add(p, vs[i]))
+}

day12.ts

@@ -0,0 +1,60 @@
+import * as fs from "fs"
+
+const input = fs.readFileSync("input-day12.txt", "utf8")
+
+function parse(input: string): Vector[] {
+    const regEx = /\<x=(-?\d+), y=(-?\d+), z=(-?\d+)\>/g
+    let m: RegExpExecArray
+    const vs = []
+    while ((m = regEx.exec(input)) !== null) {
+        vs.push([m[1], m[2], m[3]].map(Number))
+    }
+    return vs
+}
+
+type Vector = [number, number, number]
+
+function add(v1: Vector, v2: Vector): Vector {
+    return [v1[0] + v2[0], v1[1] + v2[1], v1[2] + v2[2]]
+}
+function sub(v1: Vector, v2: Vector): Vector {
+    return [v1[0] - v2[0], v1[1] - v2[1], v1[2] - v2[2]]
+}
+function sign(v1: Vector): Vector {
+    return [v1[0], v1[1], v1[2]].map(Math.sign) as Vector
+}
+function len(v1: Vector): number {
+    return v1.map(Math.abs).reduce((a, v) => a + v, 0)
+}
+
+let ps = parse(input)
+let vs = ps.map(_ => <Vector>[0, 0, 0])
+for (let i = 0; i < 1000; i++) {
+    vs = gravity()
+    ps = move()
+    console.log(`after step ${i + 1}`)
+    console.log(ps)
+    console.log(vs)
+    console.log()
+}
+
+const energy = ps.map((p, i) => len(p) * len(vs[i])).reduce((a, v) => a + v, 0)
+console.log(energy)
+
+function gravity(): Vector[] {
+    ps.forEach((p1, i) => {
+        ps.forEach((p2, j) => {
+            if (i == j) {
+                return
+            }
+
+            const v = vs[i]
+            vs[i] = add(v, sign(sub(p2, p1)))
+        })
+    })
+    return vs
+}
+
+function move() {
+    return ps.map((p, i) => add(p, vs[i]))
+}

input-day12.txt

@@ -0,0 +1,4 @@
+<x=0, y=6, z=1>
+<x=4, y=4, z=19>
+<x=-11, y=1, z=8>
+<x=2, y=19, z=15>