def anyDuplicate(arr: List[Int], k: Int): Boolean = {
    var any_duplicate = false
    val hs = mutable.HashSet[(Int, Int)]()
    arr.zipWithIndex
      .withFilter(_ => !any_duplicate)
      .map {
        case tp @ (e, idx) =>
          hs.find(_._1 == tp._1) match {
            case Some((d, idxD)) if (tp._2 - idxD <= k) =>
              any_duplicate = true  // <-------- update flag
            case Some(_) => ()
            case None =>
              hs.add(tp)
          }
      }
    any_duplicate
  }