Day 11

input/day11

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+8069 87014 98 809367 525 0 9494914 5

src/day11.scala

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+package aoc
+package day11
+
+import scala.collection.{mutable as m}
+
+val dayNumber = "11"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): String =
+  val stones = parseInput(input)
+  blink(stones, 25)
+  stones.values.sum.toString
+
+def part2(input: String): String =
+  val stones = parseInput(input)
+  blink(stones, 75)
+  stones.values.sum.toString
+
+def parseInput(input: String) =
+  input
+    .split(" ")
+    .map(_.toLong)
+    .groupBy(identity)
+    .view
+    .mapValues(_.length.toLong)
+    .to(m.Map)
+
+def changeStone(n: Long): List[Long] =
+  n.toString match
+    case "0" => List(1)
+    case s if s.length % 2 == 0 =>
+      s.splitAt(s.length / 2).toList.map(_.toLong)
+    case s => List(n * 2024)
+
+def blink(stones: m.Map[Long, Long], times: Int): Unit =
+  for (_ <- 1 to times) do
+    val changes = stones.toList.flatMap((number, count) =>
+      List((number, -count)) ++ changeStone(number).map((_, count))
+    )
+    changes.foreach((number, change) =>
+      stones.updateWith(number)(_.map(_ + change).orElse(Some(change)))
+    )