def pathFromDFSNonrec(source: V, targetPred: V => Boolean): Option[Seq[V]] = {
    // When visiting a vertex, mark it here so that it does
    // not get visited again
    val visited = scala.collection.mutable.HashSet[V]()
    // The path is constructed here
    var path: List[V] = Nil
    val stack = scala.collection.mutable.Stack[V]()
    stack.push(source)
    visited(source) = true
    path = source :: path
    while (stack.nonEmpty) {
      println(stack)
      var current = stack.pop
      if (!visited(current)) {
        visited(current) = true
        path = current :: path
      }
      val neighbourIterator = neighbours(current).toVector.reverseIterator
      while (neighbourIterator.hasNext) {
        val next = neighbourIterator.next()
        if (!visited(next)) {
          stack.push(next)
        }
      }
    }
    println("path on: " + path)
    Some(path.reverse)
  }