Question

Here’s the linked list code

public class LList
{
protected int size;
protected DNode tail, header; 

public LList()
{
    size = 0;
    tail = null;
    header = tail;
}

public void addDNode(DNode v) 
{
    // means list is empty, so add first element
    if (header == null) 
    {    
        header = v;
        tail = header;  // first element so (head == tail)
    } 
    else 
    {
        tail.setNext(v);
        v.setPrev(tail);
        v.setNext(null);
        tail = v;
    }
    size++;
}

and the remove node method that’s the problem

public DNode removeDnode(DNode current)
{
    if(current.nextNode() ==  null)
    {
        DNode previous = current.prevNode();
        previous.setNext(null);
        current.setPrev(null);
    }
    else if (current.prevNode() == null)
    {
        DNode next = current.nextNode();
        next.setPrev(null);
        current.setNext(null);
    }
    else
    {
        DNode next = current.nextNode();
        DNode previous = current.prevNode();
        previous.setNext(next);
        next.setPrev(previous);
        current.setPrev(null);
        current.setNext(null);
    }
    size = size - 1;
    return current;
}

The problem is that when I use previous.setNext(null); it won’t let me add a node again which I think it has something to do with the header and tail.

however when i use previous.setNext(tail); it doesn’t seem to remove it from the list??

Answer 1

Problem is, if you remove tail, you must move it. So try

    DNode previous = current.prevNode();
    previous.setNext(null);
    current.setPrev(null);
    tail = previous;

You have the same problem with the next—but I believe once you’re done with tail, you’ll fix it easily.