Doubly linked list, reverse()

[hamed]

Hi. I have a Doubly-linked list and i need to reverse it. I'm not sure if the method that i wrote works. It's a lil bit tricky. Would you plz correct this method if there is any thing wrong with this code?
Appreciate it

public void reverse()
{
if (first == null)
return;

DoubleNode previous = first;
DoubleNode current = first.next;
first.next = null;
while (current != null)
{
DoubleNode next = current.next;
current.next = previous;
previous = current;
current = next;
}
first = previous;
}

[joshdgreen]

Looks like it would work to me, just write some code and test away. If there are any errors, post back.

[hamed]

Thanks guys.

[m00nchile]

Why don't you take advantage of the fact you have a doubly linked list? All you would need is an additional variable to tell you what direction you're going, then all you'd need to do is change the variable that points to the first element and change direction:

public class DoublyLinkedList {
  Node first, current;
  boolean forward;
  //constructors... methods...
  
  private Node next() {
    if(forward) return current.next();
    else return current.previous();
  }
  
  public void reverse() {
    while(true) {
      if(next() == null) {
        first = current;
        forward = !forward;
        return;
      }
      current = next(); 
    }
  }
}

Also note that this example will produce errors if used like this, you'd have to check if the current element is null etc etc.

[hamed]

Thank you so much for your help, that was very useful.