feat: 2024 day 1

2024/day01.scala

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+package `2024`.day01
+
+import prelude.*
+
+def parse(s: String) = s lift { case s"$a   $b" => (a.toInt, b.toInt) }
+
+extension [A](xs: Iterable[A])
+  def counts: Map[A, Int] =
+    xs.groupMapReduce(identity)(_ => 1)(_ + _)
+
+def part1(lefts: Vector[Int], rights: Vector[Int]) =
+  (lefts.sorted zip rights.sorted).map((a, b) => (b - a).abs).sum
+
+def part2(lefts: Vector[Int], rights: Vector[Int]) =
+  (lefts.counts zipByKey rights.counts).sumBy { case (k, (a, b)) => k * a * b }
+
+@main def main() =
+  val (lefts, rights) = readInput(this).getLines.toVector.flatMap(parse).unzip
+
+  println(part1(lefts, rights))
+  println(part2(lefts, rights))

2024/day01.test.scala

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+package `2024`.day01
+
+import munit.FunSuite
+
+class Tests extends FunSuite:
+  val example = Vector(
+    "3   4",
+    "4   3",
+    "2   5",
+    "1   3",
+    "3   9",
+    "3   3",
+  )
+
+  val (lefts, rights) = example.flatMap(parse).unzip
+
+  test("part 1"):
+    assertEquals(part1(lefts, rights), 11)
+
+  test("part 2"):
+    assertEquals(part2(lefts, rights), 31)