feat: 2024 day 4

2024/day04.scala

@@ -0,0 +1,45 @@
+package `2024`.day04
+
+import prelude.*
+import utils.Size
+
+extension [A](xss: Seq[Seq[A]])
+  def rightDiagonal(size: Int): Seq[Seq[A]] = for
+    y <- 0 to xss.size - size
+    x <- size - 1 until xss(0).size
+  yield (for i <- 0 until size yield xss(y + i)(x - i))
+
+  def leftDiagonal(size: Int): Seq[Seq[A]] = for
+    y <- 0 to xss.size - size
+    x <- 0 to xss(0).size - size
+  yield (for i <- 0 until size yield xss(y + i)(x + i))
+
+  def rects(size: Size): Seq[Seq[Seq[A]]] =
+    for
+      y <- 0 to xss.size - size.height
+      x <- 0 to xss(0).size - size.width
+    yield xss.slice(y, y + size.height).map(_.slice(x, x + size.width))
+
+def anyway(x: String)(y: String): Boolean = x == y || x.reverse == y
+
+def part1(xxs: Seq[Seq[Char]]): Int =
+  def countOccurances(xs: Seq[Char]) =
+    xs.mkString.sliding(4).count(anyway("XMAS"))
+
+  (xxs ++ xxs.transpose ++ xxs.rightDiagonal(4) ++ xxs.leftDiagonal(4))
+    .sumBy(countOccurances)
+
+def part2(xxs: Seq[Seq[Char]]): Int = xxs.rects(Size(3, 3)).count {
+  case Seq(
+        Seq(a, _, b),
+        Seq(_, c, _),
+        Seq(d, _, e),
+      ) =>
+    List(s"$a$c$e", s"$b$c$d").forall(anyway("MAS"))
+}
+
+@main def main() =
+  val input = readInput(this).getLines.map(_.toVector).toVector
+
+  println(part1(input))
+  println(part2(input))