Add solution and input for 2023 day 17 (#502)

Author: stewSquared

2023/input/day17

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+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533

2023/src/day17.scala

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+package day17
+// based on solution from https://github.com/stewSquared/adventofcode/blob/src/main/scala/2023/Day17.worksheet.sc
+
+import locations.Directory.currentDir
+import inputs.Input.loadFileSync
+
+@main def part1: Unit =
+  println(s"The solution is ${search(_.nextStates)}")
+
+@main def part2: Unit =
+  println(s"The solution is ${search(_.nextStates2)}")
+
+def loadInput(): Vector[Vector[Int]] = Vector.from:
+  val file = loadFileSync(s"$currentDir/../input/day17")
+  for line <- file.split("\n")
+  yield line.map(_.asDigit).toVector
+
+enum Dir:
+  case N, S, E, W
+
+  def turnRight = this match
+    case Dir.N => E
+    case Dir.E => S
+    case Dir.S => W
+    case Dir.W => N
+
+  def turnLeft = this match
+    case Dir.N => W
+    case Dir.W => S
+    case Dir.S => E
+    case Dir.E => N
+
+val grid = loadInput()
+
+val xRange = grid.head.indices
+val yRange = grid.indices
+
+case class Point(x: Int, y: Int):
+  def inBounds = xRange.contains(x) && yRange.contains(y)
+
+  def move(dir: Dir) = dir match
+    case Dir.N => copy(y = y - 1)
+    case Dir.S => copy(y = y + 1)
+    case Dir.E => copy(x = x + 1)
+    case Dir.W => copy(x = x - 1)
+
+def heatLoss(p: Point) =
+  if p.inBounds then grid(p.y)(p.x) else 0
+
+case class State(pos: Point, dir: Dir, streak: Int, totalHeatLoss: Int):
+  def straight: State =
+    val newPos = pos.move(dir)
+    State(pos.move(dir), dir, streak + 1, totalHeatLoss + heatLoss(newPos))
+
+  def turnLeft: State =
+    val newDir = dir.turnLeft
+    val newPos = pos.move(newDir)
+    State(newPos, newDir, 1, totalHeatLoss + heatLoss(newPos))
+
+  def turnRight: State =
+    val newDir = dir.turnRight
+    val newPos = pos.move(newDir)
+    State(pos.move(newDir), newDir, 1, totalHeatLoss + heatLoss(newPos))
+
+  def nextStates: List[State] =
+    List(straight, turnLeft, turnRight).filter: s =>
+      s.pos.inBounds && s.streak <= 3
+
+  def nextStates2: List[State] =
+    if streak < 4 then List(straight)
+    else List(straight, turnLeft, turnRight).filter: s =>
+      s.pos.inBounds && s.streak <= 10
+
+  def motion = (pos, dir, streak)
+
+def search(next: State => List[State]): Int =
+  import collection.mutable.{PriorityQueue, Set}
+
+  given Ordering[State] = Ordering.by(_.totalHeatLoss)
+  val pq = PriorityQueue.empty[State].reverse
+
+  var visiting = State(Point(0, 0), Dir.E, 0, 0)
+  val visited = Set(visiting.motion)
+
+  val end = Point(xRange.max, yRange.max)
+  while visiting.pos != end do
+    val states = next(visiting).filterNot(s => visited(s.motion))
+    states.foreach(s => s"enqueuing: $s")
+    pq.enqueue(states*)
+    visited ++= states.map(_.motion)
+    visiting = pq.dequeue()
+
+  visiting.totalHeatLoss