Day 05

src/day05.scala

@@ -0,0 +1,59 @@
+package aoc
+package day05
+
+import scala.collection.mutable
+
+val dayNumber = "05"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+type Ordering = Map[Int, List[Int]]
+
+def part1(input: String): String =
+  val (ordering, pages) = parseInput(input)
+  pages
+    .filter(ps => (ps == sort(ps, ordering)))
+    .map(ps => ps(ps.length / 2))
+    .sum
+    .toString
+
+def part2(input: String): String =
+  val (ordering, pages) = parseInput(input)
+  pages
+    .map(ps => (ps, sort(ps, ordering)))
+    .collect { case (ps, sorted) if ps != sorted => sorted }
+    .map(ps => ps(ps.length / 2))
+    .sum
+    .toString
+
+def parseInput(input: String): (Ordering, List[List[Int]]) =
+  val Array(orderingInput, pagesInput) = input.split("\n\n")
+  val ordering = orderingInput
+    .split("\n")
+    .map { case s"$a|$b" => (a.toInt, b.toInt) }
+    .toList
+    .groupMap(_._1)(_._2)
+  val pages = pagesInput
+    .split("\n")
+    .toList
+    .map(_.split(",").map(_.toInt).toList)
+  (ordering, pages)
+
+def sort(pages: List[Int], ordering: Ordering): List[Int] =
+  val sorted = new mutable.ListBuffer[Int]
+  for p <- pages do
+    val placeAtIndex = ordering
+      .getOrElse(p, Nil)
+      .map(n => sorted.indexOf(n))
+      .filterNot(_ == -1)
+      .sorted
+      .headOption
+    placeAtIndex match
+      case Some(-1)        => sorted.append(p)
+      case Some(insertIdx) => sorted.insert(insertIdx, p)
+      case None            => sorted.append(p)
+  sorted.toList