70 lines
1.8 KiB
Scala
70 lines
1.8 KiB
Scala
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package aoc.day14
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import aoc._
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import scala.collection.mutable
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type Board = Seq[Seq[Char]]
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val board = lines.map(_.toSeq).toSeq
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enum Direction { case Up, Down, Left, Right }
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import Direction._
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extension (board: Board)
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inline def doTiltLeft(inline before: Board => Board, inline after: Board => Board): Board =
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after(before(board).map { col =>
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col
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.splitBy(_ == '#') // split by tilted rocks
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.map { group =>
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val (rocks, empty) = group.partition(_ == 'O')
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(rocks ++ empty).mkString
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}
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.mkString("#")
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.toSeq
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})
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def doTilt(direction: Direction): Board = direction match
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case Up => doTiltLeft(_.transpose, _.transpose)
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case Down => doTiltLeft(_.transpose.map(_.reverse), _.map(_.reverse).transpose)
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case Left => doTiltLeft(identity, identity)
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case Right => doTiltLeft(_.map(_.reverse), _.map(_.reverse))
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def cycle = Seq(Up, Left, Down, Right).foldLeft(board)(_.doTilt(_))
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def load =
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board.reverse // rows in reverse
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.zipWithIndex.map { case (row, idx) => row.count(_ == 'O') * (idx + 1L) }.sum
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// part 1
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def part1 =
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println(board.doTilt(Up).load)
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// part 2
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object Cycling:
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private val memo = mutable.Map.empty[(Board, Int), Board]
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private def getPower(b: Board, p: Int): Board = // b.cycle 2^p times
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memo.getOrElseUpdate(
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(b, p), {
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if p == 0 then b.cycle
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else getPower(getPower(b, p - 1), p - 1)
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}
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)
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def apply(b: Board, times: Long): Board =
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@scala.annotation.tailrec
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def loop(b: Board, i: Int): Board =
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val pow = 1L << i
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if pow > times then b
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else if (pow & times) > 0 then loop(getPower(b, i), i + 1)
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else loop(b, i + 1)
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loop(b, 0)
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def part2 =
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println(Cycling(board, 1_000_000_000).load)
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@main def Day14(part: Int) = part match
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case 1 => part1
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case 2 => part2
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