Make fast

aoc/src/dev/ctsk/aoc/Grid.scala

@@ -9,6 +9,7 @@ case class Point(x: Int, y: Int):
 enum Direction:
   case Up, Right, Down, Left
   def turnRight: Direction = Direction.fromOrdinal((ordinal + 1) % 4)
+  def turnLeft: Direction = Direction.fromOrdinal((ordinal - 1 + 4) % 4)
 
   def toPoint: Point =
     this match

aoc/src/dev/ctsk/aoc/days/Day12.scala

@@ -54,13 +54,16 @@ object Day12 extends Solver(12):
     plots.sizes.map((k, v) => v * plots.edges(k).length).sum
 
   def part2(plots: Plots): Int =
-    plots.sizes
-      .map((id, size) =>
-        val edge = plots.edges(id).toSet
-        val corners = edge -- edge.map((pt, dir) => (dir.turnRight(pt), dir))
-        size * corners.size
-      )
-      .sum
+    def is(pt: Point, id: Int): Boolean = plots.layout(pt).contains(id)
+    def cost(id: Int, size: Int): Int =
+      size * plots
+        .edges(id)
+        .map((pt, dir) =>
+          Seq(dir.turnLeft(pt), dir.turnRight(pt))
+            .count(adj => is(dir(adj), id) || !is(adj, id))
+        )
+        .sum / 2
+    plots.sizes.map(cost).sum
 
   override def run(input: os.ReadablePath): (Timings, Solution) =
     val grid = Grid(os.read.lines(input).map(_.toArray).toArray)