Pure `map` method using destructive operations

Map.scala

def map[A, B](xs: List[A])(f: A => B): List[B] = {
  var ys = xs
  val result = collection.mutable.Buffer.empty[B]
  while(ys != Nil) {
    result += f(ys.head)
    ys = ys.tail
  }
  result.toList
}


println(map(List(1, 2, 3))(x => x + 1)) // List(2, 3, 4)
println(map(List(1, 2, 3))(x => x * x)) // List(1, 4, 9)