Count of sign changes

// Task: given a list of Integers. Find a count of intervals with the same sign.
// Example: f(List(4, 5, -4, -5, 4, 5)) shouldBe 3

// imperative style
object ChangeSign extends App {
  def signChangeCount(list: List[Int]): Int = {
    var sum = 0
    if (list.nonEmpty) {
      var current = -list.head    // we put "-" sign to count the first interval
      for (i <- list) {
        if (i * current < 0) {
          sum += 1
          current = i
        }
      }
    }
    sum
  }

  println(signChangeCount(List.empty))                                    // 0
  println(signChangeCount(List(3, 6, 8, -2, -4, 8, 9)))                   // 3
  println(signChangeCount(List(3, 6, 8, -2, -4, 8, 9, -2, 5, -6, 0, 5)))  // 7
}



// functional style
object ChangeSign extends App {
  def signChangeCount(list: List[Int]): Int = {
    def f(list: List[Int], sum: Int, current: Int): Int = {
      list match {
        case Nil => sum
        case head :: tail if head * current < 0 => f(tail, sum+1, head)
        case head :: tail => f(tail, sum, current)
      }
    }

    f(list, 0, -list.headOption.getOrElse(0))    // we put "-" sign to count the first interval
  }


  println(signChangeCount(List.empty))                                    // 0
  println(signChangeCount(List(3, 6, 8, -2, -4, 8, 9)))                   // 3
  println(signChangeCount(List(3, 6, 8, -2, -4, 8, 9, -2, 5, -6, 0, 5)))  // 7
}