Adding day 9 part 2

day9/part2.scala

@@ -0,0 +1,60 @@
+import java.time.LocalTime
+import scala.io.StdIn.readLine
+import scala.collection.mutable.ArrayBuffer
+
+def readInput: Option[(Int, Int, Int)] = "(\\d+) players; last marble is worth (\\d+) points".r.findFirstMatchIn(readLine).map(m => (m.group(1).toInt, m.group(2).toInt, 0))
+
+val (players, lastMarbleOriginal, expected) = readInput.get
+// val (players, lastMarbleOriginal, expected) = (9, 25, 32)
+// val (players, lastMarbleOriginal, expected) = (10, 1618, 8317)
+
+val lastMarble = lastMarbleOriginal * 100
+
+case class Turn(currentPlayer: Int, marbles: Vector[Int], scores: Array[Long]) {
+  override def toString: String = s"[${currentPlayer + 1}] " + marbles.mkString(" ")
+
+  lazy val nextPlayer: Int = (currentPlayer + 1) % scores.length
+
+  def winTurn(marble: Int): Turn = {
+    val t: Vector[Int] = marbles.take(8)
+    val newMarbles: Vector[Int] = t.slice(6,7) ++ marbles.drop(8) ++ t.take(6)
+    val addScore: Long = marble + t.last
+    Turn(nextPlayer, newMarbles, updateScore(addScore))
+  }
+
+  def classicTurn(marble: Int): Turn =
+    Turn(nextPlayer, addMarble(marble), scores)
+
+  def updateScore(newScore: Long): Array[Long] = {
+    val newScores: ArrayBuffer[Long] = ArrayBuffer.concat(scores)
+    newScores(nextPlayer) += newScore
+    newScores.toArray
+  }
+
+  def addMarble(m: Int): Vector[Int] = {
+    val h = marbles.last
+    Vector(m, h) ++ marbles.dropRight(1)
+  }
+}
+
+def playGame(turn: Turn, marbleValue: Int): Turn = {
+  // Add a bit of visilibity...
+  marbleValue match {
+    case m if m % 23 == 0 => turn.winTurn(m)
+    case m => turn.classicTurn(m)
+  }
+}
+
+val turn0 = Turn(-1, Vector(0), Array.fill(players)(0))
+// Print board on each turn :
+// (1 to lastMarble).scanLeft(turn0)(playGame).foreach(println)
+
+val last = (1 to lastMarble).foldLeft((0L, turn0)) {
+  case ((max, t), m) =>
+    val newT = playGame(t, m)
+    val maxScore = newT.scores.max
+    (maxScore, newT)
+}
+
+println(s"Expected: ${expected}")
+println(s"Result: ${last._1}")