2016.18

ebowman · ebowman · commit 0423093811c1 · 2022-01-13T15:30:05.000+01:00
diff --git a/src/main/scala/y2016/Day18.scala b/src/main/scala/y2016/Day18.scala
@@ -0,0 +1,17 @@
+package y2016
+
+trait Day18 {
+
+  case class TileRow(input: String) {
+    def nextChar(x: Int): Char =
+      s"${if (x == 0) "." else input(x - 1)}${input(x)}${if (x == input.length - 1) "." else input(x + 1)}" match {
+        case "^^." | ".^^" | "^.." | "..^" => '^'
+        case _ => '.'
+      }
+
+    def next: TileRow = TileRow(input.indices.map(nextChar).mkString)
+  }
+
+  def solve(input: String, n: Int): Int =
+    Iterator.iterate(TileRow(input), n)(_.next).map(_.input.count(_ == '.')).sum
+}
diff --git a/src/test/scala/y2016/Day18Spec.scala b/src/test/scala/y2016/Day18Spec.scala
@@ -0,0 +1,14 @@
+package y2016
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should._
+
+class Day18Spec extends AnyFlatSpec with Matchers with Day18 {
+  lazy val testInput: String = util.Loader(this, "day18.txt").head
+  it should "solve part 1" in {
+    solve(testInput, 40) shouldBe 1978
+  }
+  it should "solve part 2" in {
+    solve(testInput, 400000) shouldBe 20003246
+  }
+}
