Day 06

aoc/src/dev/ctsk/aoc/Main.scala

@@ -7,7 +7,8 @@ val solvers = Map[Int, Solver](
   2 -> Day02,
   3 -> Day03,
   4 -> Day04,
-  5 -> Day05
+  5 -> Day05,
+  6 -> Day06
 )
 
 def runSolver(solver: Solver, input: os.Path): Unit =

aoc/src/dev/ctsk/aoc/days/Day06.scala

@@ -0,0 +1,64 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc._
+import scala.compiletime.ops.boolean
+import scala.util.boundary.break
+import scala.compiletime.ops.double
+
+object Day06 extends Solver(6):
+
+  def patrol(
+      grid: Array[Array[Char]],
+      start: (Int, Int)
+  ): (Boolean, () => Vector[(Int, Int)]) =
+    var seen =
+      Array.fill(4)(Array.fill(grid.length)(Array.fill(grid(0).length)(false)))
+
+    def visited() =
+      (for
+        row <- 0 until grid.length
+        col <- 0 until grid(0).length
+        if (0 until 4).exists(v => seen(v)(row)(col))
+      yield (row, col)).toVector
+
+    var dirs = Vector((-1, 0), (0, 1), (1, 0), (0, -1))
+    var dir = 0
+    var pos = start
+    seen(dir)(pos._1)(pos._2) = true
+
+    while true do
+      val next = (pos._1 + dirs(dir)._1, pos._2 + dirs(dir)._2)
+      if next._1 < 0 || next._1 >= grid.length
+        || next._2 < 0 || next._2 >= grid(0).length
+      then return (false, visited)
+      else if grid(next._1)(next._2) == '#'
+      then dir = (dir + 1) % 4
+      else if seen(dir)(next._1)(next._2)
+      then return (true, visited)
+      else
+        seen(dir)(next._1)(next._2) = true
+        pos = next
+    (false, visited)
+
+  def run(input: os.ReadablePath): (Timings, Solution) =
+    val lines = os.read.lines(input).map(_.toArray).toArray
+
+    var start =
+      (for
+        i <- 0 until lines.length
+        j <- 0 until lines(i).length
+        if lines(i)(j) == '^'
+      yield (i, j)).head
+
+    val visited = patrol(lines, start)
+    val p1 = visited._2().size
+    var p2 = 0
+    val (p2_time, _) = timed {
+      for (i, j) <- visited._2()
+      do
+        lines(i)(j) = '#'
+        if patrol(lines, start)._1 then p2 += 1
+        lines(i)(j) = '.'
+    }
+
+    return (Timings(0, 0, p2_time), Solution(Int.box(p1), Int.box(p2)))