How does traverse backward work for a Doubly Linked List in Java?

Question

My understanding of traversing backwards in a doubly linked list is traversing from some position back to the first node in the list. I have written a Doubly Linked List class in java, and a traverseBack method in it.

The code for the traverseBack method is as follows.

public void traverseBack(int d){
    for(Node n=first; n!=null; n=n.next){
        if(n.data == d){
            System.out.println("\nTraversing in Backward Direction\n");
            while(n!=null){
                System.out.println(n.data);
                n = n.prev;
            }
            return;
        }
        if(n.next==null){
            System.out.println("Given node doesn't exist");
            return;
        }
    }
}

The code was compiled and run without errors.

Can I ask whether my understanding of traversing backwards in a doubly linked list is correct or not? Is there anything in the code that I haven't done well?

Answer 1

The mistake here is you do not seem to be going backward, you're going forward. You're iterating the Node s in your for loop by calling n=n.next . Shouldn't you be calling n=n.prev ?

Why don't you just start with the last element and loop backwards from there? You could go like this:

for(Node n=last; n!=null; n=n.prev){  //this is traversing backwards now. 

Once you've done that, there's no need for the while loop at all.