等差数列

main.scala

object Main {
  def arithmeticSequence(n: Int, d: Int = 1): List[Int] = {
    require(n > 0)

    @scala.annotation.tailrec
    def f(i: Int, acc: List[Int]): List[Int] = i match {
      case 0 => acc
      case _ => f(i - 1, i * d :: acc)
    }
    f(n, Nil)
  }

  def main(args: Array[String]) {
    // List(1, 2, 3, 4, 5)
    println(arithmeticSequence(5))

    // 15
    println(arithmeticSequence(5).sum)

    // List(3, 6, 9, 12)
    println(arithmeticSequence(4, 3))

    // 30
    println(arithmeticSequence(4, 3).sum)
  }
}