[day11] solution

src/main/scala/Day11.scala

+package aoc2020
+
+import Coords._
+
+
+def day11(seatMap: Vector[Vector[Boolean]]): String =
+  val height = seatMap.size
+  val width = seatMap(0).size
+
+  val coords: Set[Coord] = for {
+    y <- (0 until height).toSet
+    x <- 0 until width
+    if seatMap(y)(x)
+  } yield Coord(y, x)
+  
+  val visibilityLOS: Coord => List[Coord] = _.lineOfSight(height, width)(coords)
+  "Basic rules (neighbours < 4)\n" +
+    gameOfSeats(occupiedAfterRound(3)(_.neighbours))(coords, Set.empty).toString +
+    "\nLOS rules (neighbours < 5)\n" + 
+    gameOfSeats(occupiedAfterRound(4)(visibilityLOS))(coords, Set.empty).toString
+  
+
+
+@annotation.tailrec
+def gameOfSeats(occupationRule: Set[Coord] => Coord => Boolean)(coords: Set[Coord], states: Set[Coord]): Int =
+  val newStates = coords.filter(occupationRule(states))
+  if newStates == states then newStates.size
+  else gameOfSeats(occupationRule)(coords, newStates)
+  
+
+
+def occupiedAfterRound(maxNeighbours: Int)(visible: Coord => List[Coord])(occupied: Set[Coord])(c: Coord) =
+  val occNeighbours = visible(c).count(occupied)
+  occNeighbours == 0 || (occupied(c) && occNeighbours <= maxNeighbours)
+
+
+object Coords {
+  opaque type Coord = (Int, Int)
+
+  extension (c: Coord)
+    def neighbours: List[Coord] = List(
+      (c._1 - 1, c._2),
+      (c._1 + 1, c._2),
+      (c._1    , c._2 - 1),
+      (c._1 - 1, c._2 - 1),
+      (c._1 + 1, c._2 - 1),
+      (c._1    , c._2 + 1),
+      (c._1 - 1, c._2 + 1),
+      (c._1 + 1, c._2 + 1),
+    )
+
+    def lineOfSight(height: Int, width: Int)(seats: Set[Coord]): List[Coord] =
+      def line(dirY: Int, dirX: Int, pos: Coord): Coord =
+        val npos = (pos._1 + dirY, pos._2 + dirX)
+        if (npos._1 >= height || npos._1 < 0 || npos._2 >= width || npos._2 < 0 || seats(npos))
+          npos
+        else
+          line(dirY, dirX, npos)
+      List(
+        line(-1,  0, c),
+        line(+1,  0, c),
+        line( 0, -1, c),
+        line( 0, +1, c),
+        line(+1, +1, c),
+        line(+1, -1, c),
+        line(-1, +1, c),
+        line(-1, -1, c),
+      )
+
+
+  def Coord(x: Int, y: Int): Coord = (x,y)
+
+  def stateToString(height: Int, width: Int)(seats: Set[Coord], states: Set[Coord]):String =
+    Vector.tabulate(height, width)((y,x) =>
+        if (!seats((y,x))) '.'
+        else if (states((y,x))) '#'
+        else 'L'
+        )
+    .map(_.mkString)
+    .mkString("\n")
+}
+
+
+

src/main/scala/Main.scala

@@ -13,6 +13,7 @@ package aoc2020
     case 8 => input()(day8)
     case 9 => input(_.toLong)(day9)
     case 10 => input(_.toInt)(day10)
+    case 11 => inputF(boolChar('L'))(Vector)(day11)
     case _ => "No such day implemented"
   }
   println(out)