Day 12

aoc/resources/day12Input.txt

@@ -0,0 +1,41 @@
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+abccccccccccccccccccaaaaaccccccaacccccaaaaaaaaaaccaaaaaaccccaaaaaccccccccccccccaaaaaaacccccccaaaaaaaaaaaaaacccaaccccccccccaacaaaaacccccccccccccccciiiijoooooouuuuuuppplllllcccccccccc
+abcccccccccccccccccaaaaaacccaacaaaaacccaaaaaaaaaccaaccaaccaaaaaacccccccccccccccaaaaaaaaccccccaaaaacccaaaaaacccaccccccccccccccaacccccccccccccccccciiiinnoooooouuxuuuupppplllllcccccccc
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+abcaaaacccccaaaaaccccccccccccaaaccaccccccccccacccaaaaaaaaaaccccccccccccccccaaaaccccccccccccccccccccccccaaaaaaaaaaaaaaaaaaccccccccaaaaaacccccaaaaaiiinnnttxxxxxxxyyyyyyvvvqqqmmmcccccc
+SbcaaaaccccccaaaaacccccaaaccccccaaacccccccccaaccaaaaaaaaaaaacccccccccccccccaaaaccccccccccccccccccccccccaaaaaaaaaaaaaaaaaacccccccaaaaaaacccccaaaaaiiinnntttxxxxEzzyyyyvvvqqqmmmdddcccc
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+abaaaaacccaaaaacccccaaacaaacccccaaaaaaccaaaaaaaaacccccccccaaaaaaccaaccacccaaaaaaaaaaaaaaaccccccaaacccccccccaaaaccccaaaaccccccccccaaaaaaaaaaaaaaccccccccccccccaaaccccccccccccccccccaaa
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+abcccccccaaaaaaaaccccaacccccccaaaaaaaaaaaaaaaaacccccccccccaaaaaccaaaaaacccccaaaaaaaaaaaaaccccaaaaaaaacccccccaacccccaaacccccccccccccaaaaaaacccccccccccccccccccccccccccccccccccccaaaaaa

aoc/src/Day12.scala

@@ -0,0 +1,91 @@
+import scala.io.Source
+
+object Day12 extends App:
+
+  val input = Source
+    .fromURL(getClass.getResource("day12Input.txt"))
+    .mkString
+    .split('\n')
+
+  val width  = input.head.length
+  val height = input.length
+
+  type Point = (Int, Int)
+  type Grid  = Map[Point, Char]
+  type Path  = List[Point]
+
+  val grid: Grid =
+    (for
+      (row, y)  <- input.zipWithIndex
+      (cost, x) <- row.zipWithIndex
+    yield (x, y) -> cost).toMap
+
+  extension (point: Point)
+    def x = point._1
+    def y = point._2
+    def neighbours: Path = List(
+      (x - 1, y),
+      (x + 1, y),
+      (x, y - 1),
+      (x, y + 1)
+    )
+    def estimateCost(to: Point): Int = (x - to.x).abs + (y - to.y).abs
+
+  extension (grid: Grid)
+    def getCost(current: Point, neighbour: Point) =
+      if grid(neighbour) - grid(current) > 1 then 100000
+      else 1
+
+    def getNeighbours(point: Point): List[Point] = point.neighbours.filter(grid.contains)
+
+    def searchShortestPath(start: Set[Point], finish: Point): Option[Path] =
+      case class PointInfo(costFromStart: Int, estimatedTotalCost: Int, shortestPath: Path)
+
+      def recur(closed: Set[Point], open: Map[Point, PointInfo]): Option[Path] =
+        val (current, PointInfo(currentCostFromStart, estimatedTotalCost, shortestPath)) =
+          open.minBy(_._2.estimatedTotalCost)
+
+        if open.isEmpty then None
+        else if current == finish then Some(shortestPath)
+        else
+          val openPoints = grid
+            .getNeighbours(current)
+            .filterNot(closed.contains)
+            .foldLeft(open - current) { case (open, neighbour) =>
+              val neighborCostFromStart = currentCostFromStart + grid.getCost(current, neighbour)
+              if open.get(neighbour).exists(_.costFromStart <= neighborCostFromStart) then open
+              else
+                open.updated(
+                  neighbour,
+                  PointInfo(
+                    neighborCostFromStart,
+                    neighborCostFromStart + neighbour.estimateCost(finish),
+                    shortestPath.appended(neighbour)
+                  )
+                )
+            }
+          recur(closed + current, openPoints)
+      recur(
+        Set(),
+        start.toList.map(it => it -> PointInfo(0, it.estimateCost(finish), List(it))).toMap
+      )
+    end searchShortestPath
+  end extension
+
+  val start = Set(grid.toList.filter(_._2 == 'S').head._1)
+  val end   = grid.toList.filter(_._2 == 'E').head._1
+
+  val gridWithElevationOnly = grid
+    .mapValues(it => if it == 'S' then 'a' else if it == 'E' then 'z' else it)
+    .toMap
+
+  val part1 = gridWithElevationOnly.searchShortestPath(start, end).map(_.length - 1)
+  println("Part 1:")
+  println(part1)
+
+  val start2 = gridWithElevationOnly.filter(_._2 == 'a').keySet
+
+  val part2 = gridWithElevationOnly.searchShortestPath(start2, end).map(_.length - 1)
+  println("Part 2:")
+  println(part2)
+end Day12