Day 7

src/day07.scala

@@ -0,0 +1,46 @@
+package aoc
+package day07
+
+val dayNumber = "07"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): Long =
+  val lines = input.split('\n')
+
+  def projectBeam(acc: (beams: Set[Int], count: Int), line: String): (Set[Int], Int) =
+    (
+      acc.beams.flatMap { beam =>
+        if line(beam) == '^' then List(beam - 1, beam + 1)
+        else List(beam)
+      },
+      acc.count + acc.beams.count(line(_) == '^')
+    )
+
+  val (_, splitCount) = lines.tail.foldLeft(Set(lines.head.indexOf('S')) -> 0)(projectBeam)
+  splitCount
+
+def part2(input: String): Long =
+  val lines = input.split('\n').toList
+
+  final case class Timeline(beam: Int, paths: Long)
+
+  def projectBeam(timelines: List[Timeline], line: String): List[Timeline] =
+    timelines
+      .flatMap(t =>
+        if line(t.beam) == '^' then
+          List(
+            Timeline(t.beam - 1, t.paths),
+            Timeline(t.beam + 1, t.paths)
+          )
+        else List(t)
+      ).groupMapReduce(_.beam)(_.paths)(_ + _)
+      .map(Timeline(_, _))
+      .toList
+
+  val timelines = lines.tail.foldLeft(List(Timeline(lines.head.indexOf('S'), 1)))(projectBeam)
+  timelines.map(_.paths).sum