PascalsTriangle.scala

// Reference: http://www.cforcoding.com/2012/01/interview-programming-problems-done.html

object PascalsTriangle {
  
  def nextrow(prev: List[Int]) :Stream[List[Int]] =  {

    val curr = collection.mutable.ArrayBuffer(1)

    for(i <- 1 until prev.length) {
      curr += prev(i - 1) + prev(i) 
    }  

    prev #:: nextrow(curr += 1 toList)  
  }
  
  lazy val pascalTriangleRows: Stream[List[Int]] = { nextrow(List(1)) }

  def printTriangle(numRows: Int) :Unit = {
    pascalTriangleRows take numRows map { _.mkString(",") } foreach println
  }
}


// scala> PascalTriangle.printTriangle(10)
// 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