102 lines
2.9 KiB
Scala
102 lines
2.9 KiB
Scala
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package aoc.day10
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import aoc._
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type Coord = (Int, Int)
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extension (c: Coord) def +(other: Coord): Coord = (c._1 + other._1, c._2 + other._2)
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enum Direction:
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case Up, Down, Left, Right
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private val directions = Array[Coord]((-1, 0), (1, 0), (0, -1), (0, 1))
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def apply(current: Coord): Coord = current + directions(ordinal)
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inline def isHorizontal = this == Left || this == Right
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inline def isVertical = !isHorizontal
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def next(pipe: Char): Option[Direction] = Some((pipe, this) match
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case ('|', _) if isVertical => this
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case ('-', _) if isHorizontal => this
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case ('L', Down) => Right
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case ('L', Left) => Up
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case ('7', Up) => Left
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case ('7', Right) => Down
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case ('J', Down) => Left
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case ('J', Right) => Up
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case ('F', Up) => Right
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case ('F', Left) => Down
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case _ => return None
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)
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object Direction:
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val all = Seq(Up, Down, Left, Right)
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def pipe(cur: Direction, next: Direction) =
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Seq('|', '-', '7', 'J', 'F', 'L').find(cur.next(_) == Some(next)).get
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val board = lines.toArray
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inline def cell(x: Coord) = board(x._1)(x._2)
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def inside(c: Coord) =
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val (x, y) = c
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x >= 0 && x < board.length && y >= 0 && y < board(x).length()
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// part1
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val (loop, sPipe) = {
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val boardSize = board.map(_.length()).sum
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// look for S
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val sCoord = (0 until board.length).findMap { x =>
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board(x).zipWithIndex.findMap { case (chr, y) => if chr == 'S' then Some((x, y)) else None }
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}.get
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@scala.annotation.tailrec
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def findCycle(accum: Seq[Coord])(current: Coord, direction: Direction): Option[(Seq[Coord], Direction)] =
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if current == sCoord then Some((accum, direction))
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else if accum.length > boardSize then None
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else
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direction.next(cell(current)) match
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case Some(nx) =>
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val nxCoord = nx(current)
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if inside(nxCoord) then findCycle(current +: accum)(nxCoord, nx) else None
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case None => None
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// find the loop
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Direction.all
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.map(d => (d(sCoord), d))
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.filter(v => inside(v._1))
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.findMap((cur, dir) =>
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findCycle(Seq(sCoord))(cur, dir)
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.map((loop, toS) => (loop.toSet, Direction.pipe(toS, dir)))
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)
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.get
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}
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def part1 =
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println(loop.size / 2)
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// part 2
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@scala.annotation.tailrec
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def loop(accum: Int)(x: Int, y: Int, insideLoop: Boolean): Int =
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if !inside((x, y)) then accum
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else if !loop.contains((x, y)) then loop(accum + (if insideLoop then 1 else 0))(x + 1, y + 1, insideLoop)
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else
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val r = if board(x)(y) == 'S' then sPipe else board(x)(y)
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loop(accum)(
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x + 1,
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y + 1,
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if Seq('|', '-', 'J', 'F').contains(r) then !insideLoop else insideLoop
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)
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def part2 =
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val res =
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(0 until board.length).map(x => loop(0)(x, 0, false)).sum
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+ (1 until board(0).length).map(y => loop(0)(0, y, false)).sum
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println(res)
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@main def Day10(part: Int) = part match
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case 1 => part1
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case 2 => part2
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