feat: 2024 day 2

2024/day02.scala

@@ -0,0 +1,24 @@
+package `2024`.day02
+
+import prelude.*
+
+def safe(xs: Seq[Int]) =
+  val isDesc = xs(0) > xs(1)
+  xs.sliding(2).forall { case Seq(a, b) =>
+    (if isDesc then a > b else a < b) && (1 to 3).contains((a - b).abs)
+  }
+
+def withoutOnes[A](xs: Seq[A]) =
+  xs.zipWithIndex.map((_, i) => xs.patch(i, Nil, 1))
+
+def part1(xss: Seq[Seq[Int]]): Int = xss.count(safe)
+
+def part2(xss: Seq[Seq[Int]]): Int =
+  xss.count(xs => safe(xs) || withoutOnes(xs).exists(safe))
+
+@main def main() =
+  val input =
+    readInput(this).getLines.map(_.split(" ").map(_.toInt).toVector).toVector
+
+  println(part1(input))
+  println(part2(input))

2024/day02.test.scala

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+package `2024`.day02
+
+import munit.FunSuite
+
+val example = Vector(
+  Vector(7, 6, 4, 2, 1),
+  Vector(1, 2, 7, 8, 9),
+  Vector(9, 7, 6, 2, 1),
+  Vector(1, 3, 2, 4, 5),
+  Vector(8, 6, 4, 4, 1),
+  Vector(1, 3, 6, 7, 9),
+)
+
+class Test extends FunSuite:
+  test("part 1"):
+    assertEquals(safe(Vector(7, 6, 4, 2, 1)), true) // decreasing by 1 or 2
+    assertEquals(safe(Vector(1, 2, 7, 8, 9)), false) // increase of 5
+    assertEquals(safe(Vector(9, 7, 6, 2, 1)), false) // decrease of 4
+    assertEquals(safe(Vector(1, 3, 2, 4, 5)), false) // not monotonic
+    assertEquals(safe(Vector(8, 6, 4, 4, 1)), false) // no change
+    assertEquals(safe(Vector(1, 3, 6, 7, 9)), true) // increasing by 1-3
+
+  test("part 1"):
+    assertEquals(part1(example), 2)
+
+  test("part 2"):
+    assertEquals(part2(example), 4)