linkedListPrintAll.swift

    //Instead of:
    func printAllKeys() {
        var current: LLNode! = head
        print("------------------")
        while (current != nil) {
            print("link item is: \(current.key)")
            current = current.next
        }
    }
    
    //what about:
    
    func printAllKeys() {
        print("------------------")
        printAllKeys(head)
    }

    func printAllKeys(previous:LLNode<T>?) {
        if let current = previous {
            print("link item is: \(current.key)")
            printAllKeys(current.next)
        }
    }