def subsetSum(numbers: List[Int], target: Int, partial: List[Int] = List.empty, partialSum: Int = 0): List[Int] = {
    if (partialSum == target) {
      partial
    } else if (partialSum >= target) {
      List.empty
    } else {
      val possibleSums = (for {
        n <- numbers
        remaining = exceptFirst(numbers, n)
      } yield subsetSum(remaining, target, partial :+ n, partialSum + n)).filter(_.nonEmpty)
      if (possibleSums.isEmpty) {
        List.empty
      } else {
        possibleSums.sortBy(_.size).head
      }
    }
  }