scala - 在 Scala 中获取一系列大小的子集？

Question

我可以获得特定大小的子集或所有子集。

scala> println((1 to 25).toSet.subsets.size)
33554432
scala> println((1 to 25).toSet.subsets(1).size)
25
scala> println((1 to 25).toSet.subsets(10).size)
1

要获得大小的子集，比如 10 或更少，我可以退回到循环并采用联合。这样做的函数式编程方式是什么？

Answer 1

您可以flatMap按如下方式使用：

(1 to 10).flatMap((1 to 25).toSet.subsets(_))

例如，下面是6 个元素subsets中大小不超过 3的所有元素的列表Set：

(1 to 3).flatMap((1 to 6).toSet.subsets(_))
// res1: scala.collection.immutable.IndexedSeq[scala.collection.immutable.Set[Int]] = Vector(
//   Set(5), Set(1), Set(6), Set(2), Set(3), Set(4),
//   Set(5, 1), Set(5, 6), Set(5, 2), Set(5, 3), Set(5, 4), Set(1, 6),
//   Set(1, 2), Set(1, 3), Set(1, 4), Set(6, 2), Set(6, 3), Set(6, 4),
//   Set(2, 3), Set(2, 4), Set(3, 4),
//   Set(5, 1, 6), Set(5, 1, 2), Set(5, 1, 3), Set(5, 1, 4), Set(5, 6, 2),
//   Set(5, 6, 3), Set(5, 6, 4), Set(5, 2, 3), Set(5, 2, 4), Set(5, 3, 4),
//   Set(1, 6, 2), Set(1, 6, 3), Set(1, 6, 4), Set(1, 2, 3), Set(1, 2, 4),
//   Set(1, 3, 4), Set(6, 2, 3), Set(6, 2, 4), Set(6, 3, 4), Set(2, 3, 4)
// )

Answer 2

我想这就是你所追求的。（使用较小的数字进行视觉验证。）

(2 to 4).flatMap(Set(1 to 5:_*).subsets)
//res0 = Vector(Set(5, 1), Set(5, 2), Set(5, 3), Set(5, 4), Set(1, 2), Set(1, 3), Set(1, 4), Set(2, 3), Set(2, 4), Set(3, 4), Set(5, 1, 2), Set(5, 1, 3), Set(5, 1, 4), Set(5, 2, 3), Set(5, 2, 4), Set(5, 3, 4), Set(1, 2, 3), Set(1, 2, 4), Set(1, 3, 4), Set(2, 3, 4), Set(5, 1, 2, 3), Set(5, 1, 2, 4), Set(5, 1, 3, 4), Set(5, 2, 3, 4), Set(1, 2, 3, 4))