mergesort.scala

def mergesort1(array: Array[Int]): Unit = {
  val helper = new Array[Int](array.length)
  mergesort2(array, helper, 0, array.length - 1)
}

private def mergesort2(array: Array[Int], helper: Array[Int], low: Int, high: Int): Unit = {
  if (low < high) {
    val middle = (low + high) / 2
    mergesort2(array, helper, low, middle)
    mergesort2(array, helper, middle + 1, high)
    merge(array, helper, low, middle, high)
  }
}