Question

I have been having some extreme difficulties with an assignment that I have been given.

The assignment is to create 4 different data structures, LinkedList, DoublyLinked list, deque, and sorted doublylinked list in java. I have almost everything except for the add method in the sorted one.

I have been trying different things for about 4 hours, and every time I do it, the test cases that I have been given fail.

I’m posting my current code, it doesn’t work how I want it to. If anyone can tell by looking at it, what I need to fix, that would be awesome. I can also post code to other methods and other things.
Thank you!

public void add(T item) {
    if (head.getData() == null) {
        head = new Node(item);
        tail = new Node(null);
        tail.setPrev(head);
        head.setNext(tail);
        count++;
    } else if (((Comparable<T>) head.getData()).compareTo(item) >=0) {
        Node tempNode = head;
        head = new Node(item);
        head.setNext(tempNode);
        tempNode.setPrev(head);
        count++;

    } else {
        Node current = head.getNext();
        for (int i = 1; i < size()  && current.getData() != null; i++) {
            if (((Comparable<T>) current.getData()).compareTo(item) > 0) {
                current = current.getNext();
            } else if  (((Comparable<T>) current.getData()).compareTo(item) <= 0) {
                Node newNode = new Node(item);
                current.getPrev().setNext(newNode);
                newNode.setNext(current);
                newNode.setNext(current.getPrev());
                current.setPrev(newNode);
                count++;
                break;
            } 
        }
        tail = new Node(item);
        current.setNext(tail);
        tail.setPrev(current);
        count++;
        return;
    }
}

EDIT ONE:

Okay, I can fix the casts thing, but that won’t exactly help what I’m trying to accomplish. Sorry about the vagueness or unclear parts about my question. It’s slightly difficult to explain.
I was also given a lot of test cases, for example this one:

 public void testAddAll() {
    SortedDLL<Integer> list = new SortedDLL<Integer>();
    assertEquals(0, list.size());

    Integer[] objects = {32,0,5125,-12};
    Integer[] sorted = {-12,0,32,5125};
    list.addAll(objects);
    assertEquals(4, list.size());

    for (int i = 0; i < objects.length; i++) {
        assertEquals(sorted[i], list.get(i));   
    }
}

When I do this one(using a system.out.println instead of assertEquals) for the last section i got :
(-12, -12)
(0, 0)
(32, 5125)
(5125, 0)
which is not quite right.
I’m just not sure what’s going on. I can’t post all of my tried solutions, because I’ve deleted most of them.

Answer 1

I find your code hard to read and comprehend. It would be nice if you posted your entire class so we know your exact variable definitions etc.

The error I could find in your code’s logic is the following:

    tail = new Node(item);
    current.setNext(tail);
    tail.setPrev(current);
    count++;
    return;

This should be changed to something like:

if ( current == tail ) {
    tail = new Node(item);
    current.setNext(tail);
    tail.setPrev(current);
    count++;
    return;
}

EDIT: The full code has been removed.