Day 9

Author: vvondra

2018/9.scala

@@ -0,0 +1,38 @@
+val numPlayers = 458
+val highestMarble = 7201900
+
+case class Turn(currentPlayer: Int, game: Seq[Int], scores: Map[Int, Long])
+
+def shiftLeft[T](sequence: Seq[T], shift: Int): Seq[T] =
+  if (shift < 0) shiftRight(sequence, Math.abs(shift))
+  else shiftRight(sequence, sequence.size - shift)
+
+def shiftRight[T](sequence: Seq[T], shift: Int): Seq[T] =
+  if (shift == 0 || sequence.isEmpty) {
+    sequence
+  }  else {
+    val split = (sequence.size - shift) % sequence.size
+    sequence.drop(split) ++ sequence.take(split)
+  }
+
+
+def printGame(turn: Turn): Unit = {
+  println(turn.game.mkString(", "))
+}
+
+val lastTurn = (0 to highestMarble).foldLeft(Turn(0, Vector.empty, Map().withDefaultValue(0))) {
+  case (Turn(currentPlayer, game, scores), marble) =>
+    val (newGame, newScores) = if (marble % 23 == 0 && marble > 0) {
+      val backSeven = shiftRight(game, 7)
+      val newScores = scores + (currentPlayer -> (scores(currentPlayer) + marble + backSeven.head))
+
+      (backSeven.drop(1), newScores)
+    } else {
+      val shifted = shiftLeft(game, 2)
+      (marble +: shifted, scores)
+    }
+
+    Turn((currentPlayer + 1) % numPlayers, newGame, newScores)
+}
+
+println(lastTurn.scores.values.max)