107 lines
3.1 KiB
Scala
107 lines
3.1 KiB
Scala
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package aoc.day17
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import aoc._
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import scala.collection.mutable
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val board = lines.map(Parser.parse(Parser.row, _).get).map(_.toArray).toArray
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val sumRows = board.map(_.scanLeft(0)(_ + _))
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val sumCols = (0 until board.length)
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.scanLeft(new Array[Int](board(0).length)) { (last, row) =>
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last.toIterator.zipWithIndex.map { (last, col) => last + board(row)(col) }.toArray
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}
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.toArray
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object Dir:
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private[Dir] val dx = Array(-1, 0, 1, 0)
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private[Dir] val dy = Array(0, 1, 0, -1)
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import Dir._
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enum Dir:
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case Up, Right, Down, Left
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def apply(x: Int, y: Int) =
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val k = this.ordinal
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(x + dx(k), y + dy(k))
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inline def times(n: Int)(x: Int, y: Int) =
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val k = this.ordinal
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val (nx, ny) = (x + n * dx(k), y + n * dy(k))
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if inside(nx, ny) then
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val dist = this match
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case Up => sumCols(x)(y) - sumCols(nx)(y)
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case Right => sumRows(x)(ny + 1) - sumRows(x)(y + 1)
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case Down => sumCols(nx + 1)(y) - sumCols(x + 1)(y)
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case Left => sumRows(x)(y) - sumRows(x)(ny)
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Some(State(nx, ny, this), dist)
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else None
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object Parser extends CommonParser:
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val digit = """\d""".r ^^ { _.toInt }
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val row = rep1(digit)
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end Parser
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inline def inside(x: Int, y: Int) =
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x >= 0 && x < board.length && y >= 0 && y < board(0).length
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case class State(x: Int, y: Int, dir: Dir):
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inline def next(ndir: Dir)(using steps: Seq[Int]) =
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steps.toIterator
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.flatMap(ndir.times(_)(x, y))
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inline def left(using Seq[Int]) = next(Dir.fromOrdinal((dir.ordinal + 3) % 4))
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inline def right(using Seq[Int]) = next(Dir.fromOrdinal((dir.ordinal + 1) % 4))
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def all(using Seq[Int]) = left ++ right
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object Walk:
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// private val visited = mutable.Map.empty[State, Int]
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private object visited:
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private inline def idx(x: Int, y: Int, dir: Dir) = x * board(0).length * 4 + y * 4 + dir.ordinal
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private val arr = Array.fill(board.length * board(0).length * 4)(1_000_000_000)
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inline def apply(s: State) = arr(idx(s.x, s.y, s.dir))
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inline def +=(inline p: (State, Int)) = p match
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case (s, v) => arr(idx(s.x, s.y, s.dir)) = v
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private val q =
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mutable.PriorityQueue.empty[(Int, State)](using scala.math.Ordering.by((v, _) => -v))
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def go()(using Seq[Int]): Option[Int] =
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Seq(Up, Down, Left, Right).foreach: dir =>
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visited += (State(0, 0, dir) -> 0)
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q += ((0, State(0, 0, dir)))
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@scala.annotation.tailrec
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def loop(): Option[Int] =
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if q.isEmpty then None
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else
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val (d, s) = q.dequeue()
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if d != visited(s) then loop()
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else if s.x == board.length - 1 && s.y == board(0).length - 1 then Some(d)
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else
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for (ns, delta) <- s.all do
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val nd = d + delta
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val old = visited(ns)
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if old > nd then
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visited += (ns -> nd)
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q += ((nd, ns))
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loop()
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var res = loop()
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res
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// part 1
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def solve(using steps: Seq[Int]) =
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val res =
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Walk
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.go()
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.get
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println(res)
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def part1 = solve(using (1 to 3))
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def part2 = solve(using (4 to 10))
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@main def Day17(part: Int) = part match
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case 1 => part1
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case 2 => part2
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