Day 2 part 1

src/main/scala/Day02.scala

@@ -0,0 +1,38 @@
+import Day02.Safety.*
+import cats.data.NonEmptyList
+import cats.syntax.all.*
+
+object Day02:
+
+  case class Level(value: Int):
+    def differsFrom(min: Int, max: Int)(that: Level): Boolean =
+      Math.abs(value - that.value) >= min && Math.abs(value - that.value) <= max
+
+  object Level:
+
+    given Ordering[Level] = Ordering.by(_.value)
+
+    def parse(s: String): Option[Level] = s.toIntOption.map(Level.apply)
+
+  enum Safety:
+    case Safe, Unsafe
+
+  case class Report(levels: NonEmptyList[Level]):
+
+    def isAllIncreasing: Boolean = levels.toList == levels.toList.sorted
+    def isAllDecreasing: Boolean = levels.toList == levels.toList.sorted.reverse
+    def areAllDeltasBetween1And3: Boolean =
+      levels.toList.zip(levels.tail).forall((l, r) => l.differsFrom(min = 1, max = 3)(r))
+
+    def safety: Safety = if ((isAllIncreasing || isAllDecreasing) && areAllDeltasBetween1And3) Safe else Unsafe
+
+  object Report:
+    def parse(s: String): Option[Report] = s.split(' ').toList.traverse(Level.parse).flatMap(_.toNel.map(Report.apply))
+
+  def parse(input: List[String]): Option[List[Report]] = input.traverse(Report.parse)
+
+  def safetyCount(input: List[String]): Option[Int] =
+    parse(input).map(_.foldMap(_.safety match
+      case Safe   => 1
+      case Unsafe => 0
+    ))

src/test/scala/Day02Suite.scala

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+import Day02.*
+import Day02Suite.*
+import cats.data.NonEmptyList
+import munit.ScalaCheckSuite
+
+class Day02Suite extends ScalaCheckSuite:
+
+  test("parsing small input"):
+    assertEquals(
+      parse(smallInput),
+      Some(
+        List(
+          NonEmptyList.of(7, 6, 4, 2, 1).map(Level.apply),
+          NonEmptyList.of(1, 2, 7, 8, 9).map(Level.apply),
+          NonEmptyList.of(9, 7, 6, 2, 1).map(Level.apply),
+          NonEmptyList.of(1, 3, 2, 4, 5).map(Level.apply),
+          NonEmptyList.of(8, 6, 4, 4, 1).map(Level.apply),
+          NonEmptyList.of(1, 3, 6, 7, 9).map(Level.apply)
+        ).map(Report.apply)
+      )
+    )
+
+  test("parsing big input returns a proper reports list"):
+    assert(parse(bigInput).isDefined)
+
+  test("safety count for small input is 2"):
+    assertEquals(safetyCount(smallInput), Some(2))
+
+  test("safety count for big input is 490"):
+    assertEquals(safetyCount(bigInput), Some(490))
+
+object Day02Suite:
+
+  val bigInput: List[String] = getLinesFromFile("src/test/scala/day02_input.txt")
+
+  val smallInput: List[String] = List(
+    "7 6 4 2 1",
+    "1 2 7 8 9",
+    "9 7 6 2 1",
+    "1 3 2 4 5",
+    "8 6 4 4 1",
+    "1 3 6 7 9"
+  )