Dado um vetor com 'n' números distintos, calcular quantas possibilidades existem para se obter a soma 's'

numbers.scala

def countSum(numbers: List[Int], expectedResult: Int): Int = {
  countSumRecursively(numbers, 0, expectedResult);
}

def countSumRecursively(numbers: List[Int], currentResult: Int, expectedResult: Int): Int = {
  if (currentResult == expectedResult)
    1
  else if ((currentResult > expectedResult) || (numbers.isEmpty))
    0
  else
    countSumRecursively(numbers, currentResult + numbers.head, expectedResult) + countSumRecursively(numbers.tail, currentResult, expectedResult);
}