Day 16: Early exit search loop

aoc/src/dev/ctsk/aoc/days/Day16.scala

@@ -3,6 +3,8 @@ package dev.ctsk.aoc.days
 import dev.ctsk.aoc.{Direction, *}
 
 import scala.collection.mutable
+import scala.util.boundary
+import scala.util.boundary.break
 
 object Day16 extends Solver(16):
   override def run(input_ : os.ReadablePath): (Timings, Solution) =
@@ -14,28 +16,40 @@ object Day16 extends Solver(16):
     val end = grid.findFirst(_ == 'E').get
 
     case class State(distance: Int, pose: Pose)
-    implicit def ord: Ordering[State] = Ordering.by(-1 * _.distance)
-
-    Direction.Up.ordinal
 
     def search(start: Pose): (Map[Pose, Int], Map[Pose, List[Pose]]) =
       val distance = mutable.Map(start -> 0)
       val ancestor = mutable.Map.empty[Pose, List[Pose]]
-      val heap = mutable.PriorityQueue(State(0, start))
+      var near = mutable.Stack(State(0, start))
+      var far = mutable.Stack.empty[State]
 
-      inline def relax(u: Pose, v: Pose, vDist: Int): Unit =
+      inline def relax(u: Pose, v: Pose, vDist: Int, isFar: Boolean): Unit =
         val oldDist = distance.getOrElse(v, 1_000_000)
         if vDist == oldDist then ancestor(v) +:= u
         if vDist < oldDist then
           ancestor(v) = List(u)
           distance(v) = vDist
-          heap.enqueue(State(vDist, v))
+          if isFar
+          then far.push(State(vDist, v))
+          else near.push(State(vDist, v))
 
-      while heap.nonEmpty do
-        val State(uDist, u) = heap.dequeue()
-        if uDist == distance(u) then
-          if !grid(u.step.pos).contains('#') then relax(u, u.step, uDist + 1)
-          for (v <- Seq(u.turnLeft, u.turnRight)) do relax(u, v, uDist + 1000)
+      boundary:
+        while near.nonEmpty do
+          var atEnd = false;
+          while near.nonEmpty do
+            val State(uDist, u) = near.pop()
+            atEnd |= u.pos == end
+            if uDist == distance(u) then
+              if !grid(u.step.pos).contains('#') then
+                relax(u, u.step, uDist + 1, false)
+              for (v <- Seq(u.turnLeft, u.turnRight)) do
+                relax(u, v, uDist + 1000, true)
+
+          if atEnd then break()
+
+          val tmp = near
+          near = far
+          far = tmp
 
       (distance.toMap, ancestor.toMap)
 
@@ -43,7 +57,7 @@ object Day16 extends Solver(16):
       search(Pose(start, Direction.Right))
     }
 
-    val endPose = DIRS.map(Pose(end, _)).minBy(distance(_))
+    val endPose = DIRS.map(Pose(end, _)).minBy(distance.getOrElse(_, 1_000_000))
 
     val p1 = distance(endPose)