Day12 JR

Day12HillClimbing.scala

import scala.annotation.tailrec

object Day12HillClimbing extends App {

    val startGrid = scala.io.Source.fromFile("./Sources/Day12HillClimbing.txt").getLines().toVector.map(_.toVector)

    val sizeY = startGrid.length
    val sizeX = startGrid(0).length

    val startPosition: (Int, Int) = (0 to sizeY-1).flatMap(y => (0 to sizeX-1).map(x => if(startGrid(y)(x)== 'S') Some(y,x) else None )).filter(_.isDefined).map(_.get)(0)
    val finishPosition: (Int, Int) = (0 to sizeY-1).flatMap(y => (0 to sizeX-1).map(x => if(startGrid(y)(x)== 'E') Some(y,x) else None )).filter(_.isDefined).map(_.get)(0)

    def update[A](vec: Vector[Vector[A]], coord: (Int,Int), value: A): Vector[Vector[A]] =
        vec.updated(coord._1, vec(coord._1).updated(coord._2, value))

    val grid: Vector[Vector[Char]] = update(update(startGrid, startPosition, 'a'), finishPosition, 'z') // remove S and E from grid

    def nextStep(accuClimbGrid: Vector[Vector[Option[Int]]]): Vector[Vector[Option[Int]]] = {
            (0 to sizeY - 1).map(y => (0 to sizeX - 1).map { x =>
                accuClimbGrid(y)(x) match {
                    case Some(a) => Some(a)
                    case None => {
                        val v = Vector(
                            (if (y-1 >= 0       && grid(y-1)(x).toInt + 1 >= grid(y)(x).toInt && accuClimbGrid(y-1)(x).isDefined) Some(accuClimbGrid(y-1)(x).get) else None),
                            (if (y+1 < sizeY    && grid(y+1)(x).toInt + 1 >= grid(y)(x).toInt && accuClimbGrid(y+1)(x).isDefined) Some(accuClimbGrid(y+1)(x).get) else None),
                            (if (x-1 >= 0       && grid(y)(x-1).toInt + 1 >= grid(y)(x).toInt && accuClimbGrid(y)(x-1).isDefined) Some(accuClimbGrid(y)(x-1).get) else None),
                            (if (x+1 < sizeX    && grid(y)(x+1).toInt + 1 >= grid(y)(x).toInt && accuClimbGrid(y)(x+1).isDefined) Some(accuClimbGrid(y)(x+1).get) else None),
                        ).filter(_.isDefined)

                        if (v.isEmpty) None else Some(v.map(_.get).min + 1) // take lowest available number_of_steps + 1 from neighbours
                    }
                }
            }.toVector).toVector
    }

    @tailrec
    def climb(accuClimbGrid: Vector[Vector[Option[Int]]]): Vector[Vector[Option[Int]]] = {
        if (accuClimbGrid(finishPosition._1)(finishPosition._2).isDefined) accuClimbGrid
        else climb(nextStep(accuClimbGrid))
    }

    // Part 1
    val climbGridPart1: Vector[Vector[Option[Int]]] = startGrid.map(y => y.map(x => if(x == 'S') Some(0) else None))
    val climbedGridPart1: Vector[Vector[Option[Int]]] = climb(climbGridPart1)
    val shortestPathPart1 = climbedGridPart1(finishPosition._1)(finishPosition._2).get

    println(s"Shortest path from Start to Finish is: ${shortestPathPart1}")

    // Part 2
    val climbGridPart2: Vector[Vector[Option[Int]]] = startGrid.map(y => y.map(x => if(x == 'S' || x == 'a') Some(0) else None))
    val climbedGridPart2 = climb(climbGridPart2)
    val shortestPathPart2 = climbedGridPart2(finishPosition._1)(finishPosition._2).get

    println(s"Shortest path from any lowest point to Finish is: ${shortestPathPart2}")
}