scala コップ本の自作distinctよりもちょっと速い自作distinct

HogeMain.scala

package ssbt

object HogeMain {

  def main(args: Array[String]) {
    val list = getRandomList(50, 500)

    println("----- start distinct1")
    repeat(10, repeatDistinct(distinct1[Int], list))

    println("----- start distinct2")
    repeat(10, repeatDistinct(distinct2[Int], list))
  }

  def repeat(num: Int, f: => Unit) {
    var start: Long = 0L
    var end: Long = 0L
    var sec: Long = 0L

    (1 to num).foreach { i =>
      start = System.currentTimeMillis

      f

      end = System.currentTimeMillis
      sec = end - start
      println("Total millisec: " + sec)
    }
  }

  def repeatDistinct(f: List[Int] => List[Int], list: List[Int]) {
    (1 to 1000).foreach { i =>
      val l = f(list)
      //val l = f(list).sorted
      //println(l)
    }
  }

  // filterを使わずcontainsで重複判定（速い）
  def distinct1[A](xs: List[A]): List[A] = {
    xs match {
      case h :: t => {
        if (t.contains(h)) distinct1(t)
        else h :: distinct1(t)
      }
      case isEmpty => xs
    }
  }

  // コップ本バージョン（遅い）
  def distinct2[A](xs: List[A]): List[A] = {
    if (xs.isEmpty) xs
    else
      xs.head :: distinct2(xs.tail.filter(x => x != xs.head))
  }

  import scala.util.Random

  def getRandomList(max: Int, length: Int): List[Int] = {
    val r = new Random
    (1 to length).map(i => r.nextInt(max)).toList
  }
  
}

----- start distinct1
Total millisec: 294
Total millisec: 211
Total millisec: 190
Total millisec: 193
Total millisec: 201
Total millisec: 198
Total millisec: 186
Total millisec: 211
Total millisec: 189
Total millisec: 188
----- start distinct2
Total millisec: 654
Total millisec: 347
Total millisec: 312
Total millisec: 314
Total millisec: 315
Total millisec: 317
Total millisec: 340
Total millisec: 361
Total millisec: 310
Total millisec: 373