Day 8

aoc/src/Day8.scala

@@ -0,0 +1,49 @@
+import scala.io.Source
+import scala.collection.mutable
+
+object Day8 extends App:
+
+  val input = Source
+    .fromURL(getClass.getResource("day8Input.txt"))
+    .mkString
+    .split('\n')
+    .map(_.map(_.asDigit).toVector)
+    .toVector
+
+  extension [T](list: IndexedSeq[T])
+    def takeUntil(predicate: T => Boolean): IndexedSeq[T] =
+      if list.indexWhere(predicate) == -1 then list
+      else list.take(list.indexWhere(predicate) + 1)
+
+  type Grid = Vector[Vector[Int]]
+
+  extension (grid: Grid)
+    def height = grid.length - 1
+    def width  = grid(0).length - 1
+
+    def allPositions =
+      for
+        y <- 0 to grid.height
+        x <- 0 to grid.width
+      yield (x, y)
+
+    def isVisible(x: Int, y: Int): Boolean =
+      val value = grid(y)(x)
+      (0 until x).forall(offset => grid(y)(offset) < value) ||
+      (0 until y).forall(offset => grid(offset)(x) < value) ||
+      (x + 1 to width).forall(offset => grid(y)(offset) < value) ||
+      (y + 1 to height).forall(offset => grid(offset)(x) < value)
+
+    def computeScenicScore(x: Int, y: Int): Int =
+      val value = grid(y)(x)
+      (x - 1 to (0, -1)).takeUntil(offset => grid(y)(offset) >= value).length *
+        (y - 1 to (0, -1)).takeUntil(offset => grid(offset)(x) >= value).length *
+        (x + 1 to width).takeUntil(offset => grid(y)(offset) >= value).length *
+        (y + 1 to height).takeUntil(offset => grid(offset)(x) >= value).length
+
+  val part1 = input.allPositions.count(input.isVisible)
+  println(s"Part 1: $part1")
+
+  val part2 = input.allPositions.map(input.computeScenicScore).max
+  println(s"Part 2: $part2")
+end Day8