InitialExercises.scala

// Initial Exercises:
 def sum(xs: List[Int]): Int = {
    def calculate(total :Int, xs: List[Int]) :Int = {
     if(xs.isEmpty) total
     else calculate((total + xs.head), xs.tail)
   }
   calculate(0,xs)
  }

 
  def max(xs: List[Int]): Int = {
    def findMax(max :Int, xs: List[Int]) :Int = {
      if (xs.isEmpty) max
      else if (max >= xs.head) findMax(max, xs.tail)
      else findMax(xs.head, xs.tail)
    }
    findMax(xs.head, xs.tail)
  }

// == Tests ==
test("sum of a few numbers") {
    assert(sum(List(1,2,0)) === 3)
  }
 
  test("sum when the list contains negative elements") {
    assert(sum(List(1,-2,5,-8)) === -4)
  }
 
  test("max of a few numbers") {
    assert(max(List(3, 7, 2)) === 7)
  }
 
  test("max when the list contains repeated elements") {
    assert(max(List(3, 17, 2,17, 16)) === 17)
  }
 
  test("max when the list contains negative elements") {
    assert(max(List(-3, -4, -10, -2, -9)) === -2)
  }
 
   test("max when the list contains only one element") {
    assert(max(List(6)) === 6)
  }
 
  test("max throws an exception if the xs List is empty") {
    intercept[NoSuchElementException] {
      max(List())
    }
  }