Create day21.scala (#786)

Author: mbovel

2024/src/day21.scala

@@ -0,0 +1,90 @@
+package day21
+
+import locations.Directory.currentDir
+import inputs.Input.loadFileSync
+
+def loadInput(): String = loadFileSync(s"$currentDir/../input/day21")
+
+case class Pos(x: Int, y: Int):
+  def +(other: Pos) = Pos(x + other.x, y + other.y)
+  def -(other: Pos) = Pos(x - other.x, y - other.y)
+  def projX = Pos(x, 0)
+  def projY = Pos(0, y)
+
+val numericalKeypad = Map(
+  '7' -> Pos(0, 0), '8' -> Pos(1, 0), '9' -> Pos(2, 0),
+  '4' -> Pos(0, 1), '5' -> Pos(1, 1), '6' -> Pos(2, 1),
+  '1' -> Pos(0, 2), '2' -> Pos(1, 2), '3' -> Pos(2, 2),
+                    '0' -> Pos(1, 3), 'A' -> Pos(2, 3),
+)
+val numericalKeypadPositions = numericalKeypad.values.toSet
+
+val directionalKeypad = Map(
+                    '^' -> Pos(1, 0), 'A' -> Pos(2, 0),
+  '<' -> Pos(0, 1), 'v' -> Pos(1, 1), '>' -> Pos(2, 1),
+)
+val directionalKeypadPositions = directionalKeypad.values.toSet
+
+
+/**********/
+/* Part 1 */
+/**********/
+
+def minPathStep(from: Pos, to: Pos, positions: Set[Pos]): String =
+  val shift = to - from
+  val h = (if shift.x > 0 then ">" else "<") * shift.x.abs
+  val v = (if shift.y > 0 then "v" else "^") * shift.y.abs
+  val reverse = !positions(from + shift.projX) || (positions(from + shift.projY) && shift.x > 0)
+  if reverse then v + h + 'A' else h + v + 'A'
+
+def minPath(input: String, isNumerical: Boolean = false): String =
+  val keypad = if isNumerical then numericalKeypad else directionalKeypad
+  val positions = if isNumerical then numericalKeypadPositions else directionalKeypadPositions
+  (s"A$input").map(keypad).sliding(2).map(p => minPathStep(p(0), p(1), positions)).mkString
+
+def part1(input: String): Long =
+  input
+    .linesIterator
+    .filter(_.nonEmpty)
+    .map: line => // 029A
+      val path1 = minPath(line, isNumerical = true) // <A^A^^>AvvvA
+      val path2 = minPath(path1) // v<<A>>^A<A>A<AAv>A^A<vAAA^>A
+      val path3 = minPath(path2) // <vA<AA>>^AvAA<^A>Av<<A>>^AvA^Av<<A>>^AA<vA>A^A<A>Av<<A>A^>AAA<Av>A^A
+      val num = line.init.toLong // 29
+      val len = path3.length() // 68
+      len * num // 211930
+    .sum
+
+@main def part1: Unit =
+  println(s"The solution is ${part1(loadInput())}")
+
+
+/**********/
+/* Part 2 */
+/**********/
+
+val cache = collection.mutable.Map.empty[(Pos, Pos, Int, Int), Long]
+def minPathStepCost(from: Pos, to: Pos, level: Int, maxLevel: Int): Long =
+  cache.getOrElseUpdate((from, to, level, maxLevel), {
+    val positions = if level == 0 then numericalKeypadPositions else directionalKeypadPositions
+    val shift = to - from
+    val h = (if shift.x > 0 then ">" else "<") * shift.x.abs
+    val v = (if shift.y > 0 then "v" else "^") * shift.y.abs
+    val reverse = !positions(from + shift.projX) || (positions(from + shift.projY) && shift.x > 0)
+    val res = if reverse then v + h + 'A' else h + v + 'A'
+    if level == maxLevel then res.length() else minPathCost(res, level + 1, maxLevel)
+  })
+
+def minPathCost(input: String, level: Int, maxLevel: Int): Long =
+  val keypad = if level == 0 then numericalKeypad else directionalKeypad
+  (s"A$input").map(keypad).sliding(2).map(p => minPathStepCost(p(0), p(1), level, maxLevel)).sum
+
+def part2(input: String): Long =
+  input
+    .linesIterator
+    .filter(_.nonEmpty)
+    .map(line => minPathCost(line, 0, 25) * line.init.toLong)
+    .sum
+
+@main def part2: Unit =
+  println(s"The solution is ${part2(loadInput())}")