scala实现归并排序

object MergedSort {
  def main(args: Array[String]) {
    def mergeSort[T] (less: (T, T) => Boolean) (input: List[T]): List[T] ={
      /**
       * @param xList 要合并的有序序列
       * @param yList 要和并的有序序列
       * @return 合并后的序列
       */
      def merge(xList: List[T], yList: List[T]): List[T] =
        (xList, yList) match {
          case (Nil, _) => yList
          case (_, Nil) => xList
          case (x :: xtail, y :: ytail) =>
            if (less(x, y)) x :: merge(xtail, yList)
            else y :: merge(xList, ytail)
        }
      val n = input.length / 2
      if (n == 0) input
      else {
        val (x, y) = input splitAt n        //把要排序的input均分成两个列表   
        merge(mergeSort(less)(x), mergeSort(less)(y))   //先对分后的两个列表进行归并排序,在对排序好的有序列表进行归并
      }

      println(mergeSort((x: Int, y: Int) => x < y)(List(3, 7, 9, 5)))
      val reversed_mergedsort = mergeSort((x: Int, y: Int) => x > y) _
      println(reversed_mergedsort(List(3,7,9,5)))
    }
  }
}