Day 4

src/day04.scala

@@ -0,0 +1,58 @@
+package aoc
+package day04
+
+import scala.collection.mutable
+
+val dayNumber = "04"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): String =
+  input
+    .split('\n')
+    .map { case s"$_: $winning | $numbers" =>
+      (
+        winning.split(" ").flatMap(_.toIntOption),
+        numbers.split(" ").flatMap(_.toIntOption)
+      )
+    }
+    .map((w, n) => w.intersect(n).length)
+    .filter(_ > 0)
+    .map(l => Math.pow(2, l - 1).toInt)
+    .sum
+    .toString
+
+def part2(input: String): String =
+
+  final case class Card(
+      matchingCards: List[Int],
+      instances: Int = 1
+  ):
+    def addInstances(n: Int) = copy(instances = instances + n)
+
+  val cards =
+    input
+      .split('\n')
+      .map { case s"$_: $winning | $numbers" =>
+        winning
+          .split(" ")
+          .flatMap(_.toIntOption)
+          .intersect(numbers.split(" ").flatMap(_.toIntOption))
+          .length
+      }
+      .zipWithIndex
+      .map((count, index) => Card((1 to count).map(_ + index).toList))
+      .to(mutable.ArraySeq)
+
+  for card <- cards do
+    for index <- card.matchingCards do
+      cards.update(index, cards(index).addInstances(card.instances))
+
+  cards
+    .map(_.instances)
+    .sum
+    .toString