80 lines
1.3 KiB
Swift
80 lines
1.3 KiB
Swift
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struct Moon: Hashable {
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var x: Int
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var y: Int
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var z: Int
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var vx = 0
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var vy = 0
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var vz = 0
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init(x: Int, y: Int, z: Int) {
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self.x = x
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self.y = y
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self.z = z
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}
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mutating func move() {
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x += vx
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y += vy
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z += vz
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}
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mutating func applyGravity(from other: Moon) {
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vx += grav(x, other.x)
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vy += grav(y, other.y)
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vz += grav(z, other.z)
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}
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var energy: Int {
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let pot = abs(x) + abs(y) + abs(z)
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let kin = abs(vx) + abs(vy) + abs(vz)
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return pot * kin
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}
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}
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func grav(_ a: Int, _ b: Int) -> Int
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{
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if a < b {
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return 1
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} else if a == b {
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return 0
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} else {
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return -1
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}
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}
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var moons = [
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Moon(x: -13, y: 14, z: -7),
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Moon(x: -18, y: 9, z: 0),
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Moon(x: 0, y: -3, z: -3),
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Moon(x: -15, y: 3, z: -13)
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]
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@discardableResult
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func step() -> Int {
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for a in 0..<moons.count {
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for b in 0..<moons.count where a != b {
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moons[a].applyGravity(from: moons[b])
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}
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}
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var energy = 0
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for i in 0..<moons.count {
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moons[i].move()
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energy += moons[i].energy
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}
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return energy
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}
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var seen: Set<[Moon]> = []
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var steps = 0
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repeat {
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seen.insert(moons)
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step()
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steps += 1
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} while !seen.contains(moons)
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