pascal.scala

object pascal {

  private def get(rows: List[Long], index: Int): Long = {
    if (index < 0 || index >= rows.length) 0L
    else rows(index)
  }

  private def row(prev: List[Long] = List()): List[Long] = {
    if (prev.isEmpty) List(1)
    else (0 to prev.size).map { i => get(prev, i - 1) + get(prev, i) }.toList
  }

  def triangleRow(n: Long): List[Long] =
    (0L until n).foldLeft(List.empty[Long]) { (prev, _) => row(prev) }

  def triangleRows(n: Long): List[List[Long]] =
    (0L until n).foldLeft(List[List[Long]]()) { (prev, _) =>
      prev :+ row(prev.lastOption.getOrElse(List()))
    }

  def drawTriangle(n: Long): Unit = {
    triangleRows(n).foreach { row =>
      row.foreach { n => print(f"$n%4d") }
      println
    }
  }
}

object Main extends App { pascal.drawTriangle(8) }