Last active
July 12, 2022 11:00
-
-
Save stewSquared/1798cf58f990c76e36386aeb9666c6ff to your computer and use it in GitHub Desktop.
Playing with Scala 3 opaque types for AoC 2021 Day 17
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
val input = io.Source.fromResource("2021/day-17-1.txt").getLines.next() | |
case class Point(x: Int, y: Int) | |
object Point: | |
opaque type Position <: Point = Point | |
opaque type Velocity <: Point = Point | |
opaque type Origin <: Position = Position | |
def Position(x: Int, y: Int): Position = Point(x, y) | |
def Velocity(x: Int, y: Int): Velocity = Point(x, y) | |
final val Origin: Origin = Point(0, 0) | |
extension (p: Position) def move(v: Velocity) = Position(p.x + v.x, p.y + v.y) | |
extension (v: Velocity) def drag = Velocity(v.x - v.x.sign, v.y - 1) | |
import Point.* | |
case class Area(left: Int, right: Int, bot: Int, top: Int): | |
def contains(pos: Position) = | |
(left to right).contains(pos.x) && (bot to top).contains(pos.y) | |
type Trajectory = Seq[Position] | |
extension (trajectory: Trajectory) | |
def highest = trajectory.maxBy(_.y).y | |
def hits(target: Area) = trajectory.exists(target.contains) | |
case class Probe(pos: Position, vel: Velocity): | |
def step = copy(pos.move(vel), vel.drag) | |
def missed(a: Area): Boolean = | |
val falling = vel.y < 0 | |
val vertical = vel.x == 0 | |
val short = pos.x < a.left | |
val below = pos.y < a.bot | |
val beyond = pos.x > a.right | |
short && vertical || below && falling || beyond | |
object Probe: | |
def fire(vel: Velocity) = new reflect.Selectable { | |
def at(target: Area): Trajectory = | |
val start = Probe(Point.Origin, vel) | |
val steps = Iterator.iterate(start)(_.step) | |
steps.takeWhile(!_.missed(target)).map(_.pos).toSeq | |
} | |
val target = input match | |
case s"target area: x=$left..$right, y=$bot..$top" => | |
Area(left.toInt, right.toInt, bot.toInt, top.toInt) | |
import target.{left, right, bot} | |
val launches = for | |
x <- math.sqrt(left).toInt to right | |
y <- bot.abs to bot by -1 | |
trajectory = Probe fire Velocity(x, y) at target | |
if trajectory hits target | |
yield trajectory | |
val ans1 = launches.head.highest | |
val ans2 = launches.size |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
(This problem was entirely solvable with a few lines of pen and napkin math, but I thought it might be interesting for playing with some Scala 3 features)