Pascal Triangle

PascalTri.scala

object PascalTri {
  def triangle(level: Int): List[List[Int]] = {
    def triGen(loop: Int, xs: List[Int], acc: List[List[Int]]): List[List[Int]] =
      if (loop == 0) acc
      else {
        val ts = 1 +: xs.sliding(2).map(_.sum).toList :+ 1
        triGen(loop - 1, ts, acc :+ ts)
      }
    triGen(level - 2, List(1, 1), List(List(1), List(1, 1)))
  }

  def main(args: Array[String]): Unit =
    prettyPrint(triangle(args(0).toInt)))

  def prettyPrint(triangle: List[List[Int]]): Unit = {
    def _pp(xs: List[List[Int]], balance: Int): Unit = {
      if (balance == 0) println() else {
        println(s"${" " * (balance - 1)}${xs.head.mkString(" ")}")
        _pp(xs.tail, balance - 1)
      }
    }

    _pp(triangle, triangle.size)
  }
}

/* REPL Output

scala> import Solution._

scala> prettyPrint(triangle(5))
    1
   1 1
  1 2 1
 1 3 3 1
1 4 6 4 1

scala> prettyPrint(triangle(15))
              1
             1 1
            1 2 1
           1 3 3 1
          1 4 6 4 1
         1 5 10 10 5 1
        1 6 15 20 15 6 1
       1 7 21 35 35 21 7 1
      1 8 28 56 70 56 28 8 1
     1 9 36 84 126 126 84 36 9 1
    1 10 45 120 210 252 210 120 45 10 1
   1 11 55 165 330 462 462 330 165 55 11 1
  1 12 66 220 495 792 924 792 495 220 66 12 1
 1 13 78 286 715 1287 1716 1716 1287 715 286 78 13 1
1 14 91 364 1001 2002 3003 3432 3003 2002 1001 364 91 14 1
*/