DeliveryHero_task2.scala

sealed trait Slice extends Product with Serializable {
    def length: Int
  }
  object Slice {
    def empty: Slice = EmptySlice
  }

  case class HalfSlice(num: Int, ind: Int) extends Slice {
    override def length = 1
  }

  case class FullSlice(even: Int, odd: Int, length: Int) extends Slice {
    def isBelongsToSlice(num: Int, ind: Int) = if (ind % 2 == 0) num == this.even else num == this.odd

    def increaseLength: FullSlice = this.copy(length = length + 1)
  }

  case object EmptySlice extends Slice {
    override def length = 0
  }

  def maxSwitch(a: Array[Int]): Int = if (a.length < 3) a.length else {
    val (prevMaxLen, lastSlice) = a.zipWithIndex.foldLeft(0 -> Slice.empty) {
      case ((maxSliceLen, EmptySlice), (num, ind)) =>
        Math.max(maxSliceLen, 1) -> HalfSlice(num, ind)

      case ((maxSliceLen, HalfSlice(sNum, sInd)), (num, ind)) =>
        Math.max(maxSliceLen, 2) -> (
          if (sInd % 2 == 0) FullSlice(sNum, num, 2) else FullSlice(num, sNum, 2)
        )

      case ((maxSliceLen, slice@FullSlice(even, odd, sLen)), (num, ind)) if slice.isBelongsToSlice(num, ind) =>
        if (slice.length + 1 > maxSliceLen) (sLen + 1) -> slice.increaseLength
        else maxSliceLen -> slice.increaseLength

      // new num does't belongs to current slice
      case ((maxSliceLen, slice@FullSlice(even, odd, sLen)), (num, ind)) =>
        Math.max(maxSliceLen, 2) -> (
          if (ind % 2 == 0) FullSlice(num, odd, 2) else FullSlice(odd, num, 2)
        )

      case x => sys.error(s"something went wrong: $x")
    }
    Math.max(prevMaxLen, lastSlice.length)
  }