AoC Day12 Part1 - WIP

object Day12 {
  def part1(input: Iterator[String]): String = {
    val grid = input.toIndexedSeq
    val startAndEnd = grid.zipWithIndex.flatMap { case (row, i) =>
      row.zipWithIndex.flatMap { case (v, j) =>
        if (v == 'S') Some((v, i, j))
        else if (v == 'E') Some((v, i, j))
        else None
      }
    }
    val heights = grid.map {
      _.map { v =>
        if (v == 'S') 'a'
        else if (v == 'E') 'z'
        else v
      }.map(_ - 'a')
    }
    val start = startAndEnd.find(_._1 == 'S').get
    val end = startAndEnd.find(_._1 == 'E').get
    val path = scala.collection.mutable.IndexedSeq.fill[Option[Int]](heights.size, heights(0).size)(None)
    val toVisit = scala.collection.mutable.Queue((start._2, start._3, 0))
    var found = -1
    var maxH = -1
    var minD = -1

    def isValid(i: Int, j: Int): Boolean = i >= 0 && i < grid.size && j >= 0 && j < grid(0).size

    while (toVisit.nonEmpty && found == -1) {
      val (y, x, d) = toVisit.removeHead()
      if (y == end._2 && x == end._3) found = d
      if (path(y)(x).isEmpty) {
        path(y)(x) = Some(d)
        val h = heights(y)(x)
        if (maxH < h) {
          maxH = h
          minD = d
        }
        Seq((-1, 0), (1, 0), (0, 1), (0, -1)).foreach { case (i, j) =>
          if (isValid(y + i, x + j)) {
            if ((heights(y + i)(x + j) - h).abs <= 1 && path(y + i)(x + j).isEmpty) {
              toVisit.append((y + i, x + j, d + 1))
            }
          }
        }
      }
    }
    // Added the minD and Math.max here in case it would accept the shortest path to the highest reachable point...
    Math.max(found, minD).toString
  }
}