在Scala中获取一系列大小的子集？

import scala.collection.mutable.ListBuffer

def getSubsetsOfSize[T](set: List[T], size: Int): List[List[T]] = {
  val subsets = ListBuffer[List[T]]()
  val subset = ListBuffer[T]()

  def backtrack(start: Int, subsetSize: Int): Unit = {
    if (subsetSize == size) {
      subsets += subset.toList
      return
    }

    for (i <- start until set.length) {
      subset += set(i)
      backtrack(i + 1, subsetSize + 1)
      subset.remove(subsetSize)
    }
  }

  backtrack(0, 0)
  subsets.toList
}

val set = List(1, 2, 3, 4)
val size = 2
val subsets = getSubsetsOfSize(set, size)
subsets.foreach(println)