Advent of Code Day 17 2021 using named tuples

day17-aoc-2021.scala

//> using scala "3.4.0-RC1-namedtuples-bin-SNAPSHOT"
// original solution taken from https://scalacenter.github.io/scala-advent-of-code/puzzles/day17#final-code (by @bishabosha)

import scala.language.experimental.namedTuples

type Target = (xs: Range, ys: Range)
type Point  = (x: Int, y: Int)
type Probe  = (position: Point, velocity: Point)

val initial = (x = 0, y = 0)

def step(probe: Probe): Probe =
  val (pos, vel) = probe
  (
    position = (x = pos.x + vel.x,      y = pos.y + vel.y),
    velocity = (x = vel.x - vel.x.sign, y = vel.y - 1)
  )

def collides(probe: Probe, target: Target): Boolean =
  val (pos, _) = probe
  val (xs, ys) = target
  xs.contains(pos.x) && ys.contains(pos.y)

def beyond(probe: Probe, target: Target): Boolean =
  val (pos, vel) = probe
  val (xs, ys) = target
  val beyondX = (vel.x == 0 && pos.x < xs.min) || pos.x > xs.max
  val beyondY = vel.y < 0 && pos.y < ys.min
  beyondX || beyondY

def simulate(probe: Probe, target: Target): Option[Int] =
  LazyList
    .iterate((probe, 0))({ case (probe @ (pos, _), maxY) => (step(probe), maxY `max` pos.y)})
    .dropWhile((probe, _) => !collides(probe, target) && !beyond(probe, target))
    .headOption
    .collect { case (probe, maxY) if collides(probe, target) => maxY }

def allMaxHeights(target: Target)(positiveOnly: Boolean): Seq[Int] =
  val (xs, ys) = target
  val upperBoundY = ys.min.abs
  val lowerBoundY = if positiveOnly then 0 else -upperBoundY
  for
    vx <- 0 to xs.max
    vy <- lowerBoundY to upperBoundY
    maxy <- simulate((position = initial, velocity = (x = vx, y = vy)), target)
  yield
    maxy

type Parser[A] = PartialFunction[String, A]

val IntOf: Parser[Int] =
  case s if s.matches(raw"-?\d+") => s.toInt

val RangeOf: Parser[Range] =
  case s"${IntOf(begin)}..${IntOf(end)}" => begin to end

val Input: Parser[Target] =
  case s"target area: x=${RangeOf(xs)}, y=${RangeOf(ys)}" => (xs, ys)

def part1(input: String) =
  allMaxHeights(Input(input.trim))(positiveOnly = true).max

def part2(input: String) =
  allMaxHeights(Input(input.trim))(positiveOnly = false).size

@main def p1 = println(s"the solution is ${part1(INPUT)}")
@main def p2 = println(s"the solution is ${part2(INPUT)}")

val INPUT = "target area: x=201..230, y=-99..-65"