Solve 2020 day 23 part 1

sim642 · sim642 · commit 13067e325b9e · 2020-12-23T10:13:16.000+02:00
diff --git a/src/main/scala/eu/sim642/adventofcode2020/Day23.scala b/src/main/scala/eu/sim642/adventofcode2020/Day23.scala
@@ -0,0 +1,38 @@
+package eu.sim642.adventofcode2020
+
+import eu.sim642.adventofcodelib.IteratorImplicits._
+import eu.sim642.adventofcodelib.SeqImplicits._
+import eu.sim642.adventofcodelib.IntegralImplicits._
+
+object Day23 {
+
+  type Cups = Vector[Int]
+
+  def simulateMove(cups: Cups): Cups = {
+    val (current +: picked, rest) = cups.splitAt(4)
+    val destination = Iterator.from(current - 1, -1).map(_ %+ 10).find(rest.contains).get
+    val (beforeDestination, afterDestination) = rest.splitAt(rest.indexOf(destination) + 1)
+    val newRest = beforeDestination ++ picked ++ afterDestination
+    (current +: newRest).rotateLeft(1)
+  }
+
+  def simulateMoves(cups: Cups, moves: Int = 100): Cups = {
+    Iterator.iterate(cups)(simulateMove)(moves)
+  }
+
+  def simulateMovesLabels(cups: Cups, moves: Int = 100): String = {
+    val finalCups = simulateMoves(cups, moves)
+    val 1 +: restCups = finalCups.rotateLeft(finalCups.indexOf(1))
+    restCups.mkString("")
+  }
+
+
+  def parseCups(input: String): Cups = input.map(_.asDigit).toVector
+
+  //lazy val input: String = io.Source.fromInputStream(getClass.getResourceAsStream("day23.txt")).mkString.trim
+  val input: String = "318946572"
+
+  def main(args: Array[String]): Unit = {
+    println(simulateMovesLabels(parseCups(input)))
+  }
+}
diff --git a/src/test/scala/eu/sim642/adventofcode2020/Day23Test.scala b/src/test/scala/eu/sim642/adventofcode2020/Day23Test.scala
@@ -0,0 +1,20 @@
+package eu.sim642.adventofcode2020
+
+import Day23._
+import org.scalatest.funsuite.AnyFunSuite
+
+class Day23Test extends AnyFunSuite {
+
+  val exampleInput = "389125467"
+
+  test("Part 1 examples") {
+    assert(simulateMove(parseCups(exampleInput)) == parseCups("289154673"))
+
+    assert(simulateMovesLabels(parseCups(exampleInput), 10) == "92658374")
+    assert(simulateMovesLabels(parseCups(exampleInput)) == "67384529")
+  }
+
+  test("Part 1 input answer") {
+    assert(simulateMovesLabels(parseCups(input)) == "52864379")
+  }
+}
