add answers to exercise 1-7 chapter 3

[ryblovAV]

Hi @axel22, pls check this answers

[axel22]

You can require that this method is tail recursive, to avoid the danger of a stack overflow.

[axel22]

Thanks for the PR!
I've left mostly minor comments, except the concurrent sorted list exercise -- there the goal is to implement an actual mutable linked list, in which tail references are AtomicReference objects.

[ryblovAV]

Hi @axel22,
Thanks for replying
pls see my changes

P.S.
I also have added the answers to the exercise 1-8 for chapter 4,
pls see

[axel22]

I would model the list with the following inner class:

class Node(val head: T) {
  val tail = new AtomicReference[Option[Node]](None)
}

The ConcurrentSortedList would then contain a single reference:

val root = AtomicReference[Option[Node]](None)

This would make the implementation of the add method simpler, and easier to reason about. There would be no need to call set in addToTail, since you set it only once anyway.

[ryblovAV]

Thanks for replying,
I'll try to fix code according to your recommendations

[ryblovAV]

Hi @axel22 ,
pls see

[axel22]

LGTM - thanks a lot for following up!

[ryblovAV]

thank you for your time