Need help with Scala code block please. Will upvote answer:

object subtyping { // Instances of Counter have a integer field that can be incremented, decremented, or read. class Counter { private var n = 0 def increment () = { n = n + 1 } def decrement () = { n = n - 1 } def get () : Int = n } 

 // EXERCISE 2: complete the following function. // It is the same as observeCounter except that f has a parameter of type List[Counter] not Counter. // f will insist that the List[Counter] has length 3. // You must return a List[Int] not an Int. // The first element of the result List[Int] must correspond to the number of times that increment/decrement were called on the first element of type List[Counter], similarly for the second and third elements. def observeCounterList (f : List[Counter] => Unit) : List[Int] = { // TODO: Provide definition here. List (-1, -1, -1) }