object test{
  def main(args: Array[String]): Unit = {
    println("Hello Spark")

    val arrayBuffer=ArrayBuffer[Int](1,2,3,5,9,12)

    val out = arrayBuffer.indices.map(index => {
      val x1 = index - 1
      val x2 = index
      index match {
        // 头节点单独处理，其余元素根据下标从数组中取值进行计算
        case index if 1 until arrayBuffer.length contains index => (index, arrayBuffer.apply(x2)- arrayBuffer.apply(x1))
        case _ => (index, 0)
      }
    })
    out.foreach(println)
  }

}

Hello Spark
(0,0)
(1,1)
(2,1)
(3,2)
(4,4)
(5,3)