S99 P15

S99P15.scala

/*
 *  S99 P15 http://aperiodic.net/phil/scala/s-99/
 *  (**) Duplicate the elements of a list a given number of times.
 *  
 *  Example:
 *  
 *  scala> duplicateN(3, List('a, 'b, 'c, 'c, 'd))
 *  res0: List[Symbol] = List('a, 'a, 'a, 'b, 'b, 'b, 'c, 'c, 'c, 'c, 'c, 'c, 'd, 'd, 'd)
 */

object S9915 extends App {

  //with flatmap
  def duplicateN[A](n: Int, l: List[A]): List[A] = l flatMap { List.fill(n)(_) }

  val r = duplicateN(3, List('a, 'b, 'c, 'c, 'd))

  assert(r == List('a, 'a, 'a, 'b, 'b, 'b, 'c, 'c, 'c, 'c, 'c, 'c, 'd, 'd, 'd))

  //--------------------------------

  //flatmap is map + flatten
  def duplicateN2[A](n: Int, l: List[A]): List[A] = {
    val ll: List[List[A]] = l.map({ i: A => List.fill(n)(i) })
    ll.flatten
  }

  val r2 = duplicateN2(3, List('a, 'b, 'c, 'c, 'd))
  assert(r2 == List('a, 'a, 'a, 'b, 'b, 'b, 'c, 'c, 'c, 'c, 'c, 'c, 'd, 'd, 'd))
  
}