Day 13

src/day13.scala

@@ -0,0 +1,54 @@
+package aoc
+package day13
+
+val dayNumber = "13"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def transpose(grid: List[String]): List[String] =
+  List.tabulate(grid.head.length)(x =>
+    Array.tabulate(grid.length)(y => grid(y)(x)).mkString
+  )
+
+def part1(input: String): String =
+  def findReflection(rows: List[String]): Option[Int] =
+    (1 until rows.length).find(i =>
+      val (up, down) = rows.splitAt(i)
+      up.reverse.zip(down).forall(_ == _)
+    )
+
+  input
+    .split("\n\n")
+    .map(_.split('\n').toList)
+    .flatMap(pattern =>
+      findReflection(pattern)
+        .map(_ * 100)
+        .orElse(findReflection(transpose(pattern)))
+    )
+    .sum
+    .toString
+
+def part2(input: String): String =
+  def findReflection(rows: List[String]): Option[Int] =
+    (1 until rows.length).find(i =>
+      val (up, down) = rows.splitAt(i)
+      val linesToCompare = up.reverse.zip(down)
+      val area = linesToCompare.length * linesToCompare.head._1.length
+      val differencesCount = linesToCompare.map(_.zip(_).count(_ == _)).sum
+      area - differencesCount == 1
+    )
+
+  input
+    .split("\n\n")
+    .map(_.split('\n').toList)
+    .flatMap(pattern =>
+      findReflection(pattern)
+        .map(_ * 100)
+        .orElse(findReflection(transpose(pattern)))
+    )
+    .sum
+    .toString