Insert into Doubly LinkedList in reverse lexicographical order

[raihan26]

I am tring to insert string into doubly linked list in reverse lexicographical order. But I am not sure how can I maintain the insertion order in reverse lexicographical order.

Meaning- **You can add elements to a linked list. When you add a new string to the list it is maintained in reverse lexicographical order without using any library.**

This is my below code.

theList.insertReverseLexicographicalOrder("B");
    theList.insertReverseLexicographicalOrder("A");
    theList.insertReverseLexicographicalOrder("H");
    theList.insertReverseLexicographicalOrder("D");
    theList.insertReverseLexicographicalOrder("E");

	public void insertReverseLexicographicalOrder(String dd) {
		Link newLink = new Link(dd);
		if (isEmpty()){
			last = newLink;
		}else{
                     Link focus = first; 
                     // This part is right or not?
			while(focus.next != null && dd.compareToIgnoreCase(focus.next.iData) > 0) { 
			    focus = focus.next; 
			} 
//What to do now as I am not able to understand... Any help will be appreciated..
			first.previous = newLink;
		}
		newLink.next = first;
		first = newLink;
	}

    class Link {
    	public String iData;
    	public Link next;
    	public Link previous;
    
    	public Link(String id) {
    		iData = id;
    	}
    
    	public String toString() {
    		return "{" + iData + "} ";
    	}
    }

      

      

    private Link first;
    	private Link last;
    
    	public DoublyLinkedList() {
    		first = null;
    		last = null;
    	}

The problem that I am having with my code is that it is not working with that while loop that I have added in my code.. Any suggestions will be appreciated with some code based on my solution..

[Norm]

problem that I am having with my code is that it is not working with that while loop

Can you explain what happens and what the problem is?

Try debugging the code by adding some printlns to show the values of the variables that are being used in the while loop. The print out should help you understand what the code is doing.

[raihan26]

Thanks for replying back. As I am not sure whether my code is working fine. Since the logic that I am using with that it is not working fine. My questions is I want to insert node into doubly linked list such that-
You can add elements to a linked list. When you add a new string to the list it is maintained in reverse lexicographical order without using any library.
This is my question..

[Norm]

I think the answer to your question is: Yes it can be done.

What is a "library"?

[raihan26]

By Library I mean without using any sort kind of thing.. Any solution with my code will really help me a lot.. Thanks

[Norm]

Have you used a piece of paper and pencil to work out the logic for traversing the list and finding the insert point and then doing the insert? I have always had to do it that way.

For debugging I use lots of printlns to show the values of the variables as the code executes. The output will show you what your code is doing.

[raihan26]

Yeah I did that. But I am not able to know from where should I start. If you can help me in that. It will be of great help to me.. So by that way I will be able to understand whole thing where I am lacking.

[Norm]

where should I start.

Add lots of printlns to show you the values of the variables as the while loop excutes etc
Be sure to add an id String to each print out so you can tell where it was printed.
Execute the code and copy the print out here with your questions about why the code is doing what it is doing.

[raihan26]

I have updated the whole code. But still I am having some problem. Any suggestions will be appreciated..

**Updated Code:-**

    class DoublyLinkedList {
    	private Link root;
    	private Link first;
    
    	public DoublyLinkedList() {
    		root = null;
    		first = null;
    	}
    
    	public boolean isEmpty() {
    		return root == null;
    	}

    public void insertReverseLexicographicalOrder(String dd) {
    		Link newLink = new Link(dd);
    		Link focus = first; 
    		if (isEmpty()){
    			root = newLink;
    			newLink.previous = null;
    			newLink.next = null;
    		}else{
    
    	while(focus.next != null && dd.compareToIgnoreCase(focus.next.iData) > 0) 
    			      focus = focus.next; 
    
    			
    			newLink.next = focus;
    			focus.previous = newLink;
    			
    		}
    		first = newLink;
    	}

[Norm]

I don't see any printlns. How are you debugging the code?

[raihan26]

I am debugging the code using eclipse debugger. I just wanted to see why my logic is not working correctly..

[Norm]

I can't help you when you use the debugger.
Did you see where the problem is?