Shortest labyrinth path

labyrinth.scala

type Point = (Int, Int)
case class StateVars(pathLength: Int, seen: Set[Point], starts: Set[Point])
// lab is 2-dimension array either of enterable cell (true) or obsticle (false)
def solve(start: Point, end: Point, lab: Vector[Vector[Boolean]]): Int = {
  State[StateVars, Boolean] { case StateVars(pathLength, seen, expandFrom) =>
    val nextArea = expandFrom.flatMap { case (x, y) =>
      Set((x - 1, y), (x + 1, y), (x, y + 1), (x, y - 1)).filterNot(seen).filter {
        case (nx, ny) => nx >= 0 && nx < lab.size && ny >=0 && ny < lab(0).size && lab(nx)(ny)
      }
    }
    (StateVars(pathLength + 1, seen ++ expandFrom, nextArea), nextArea(end))
  }.iterateWhile(!_).runS(StateVars(0, Set.empty, Set(start))).value.pathLength
}