Java Binary Search Tree Recursive Copy Tree

Question

I'm working on a problem which requires me to copy a binary search tree recursively and to return the tree. I am coding in the binary search tree class, so it will copy whatever binary search tree it is called on. The requirements say that the private method must have a return type of Entry<E> and a parameter of type Entry<E> . The problem I'm running into is getting multiple entries added to the tree.

Here is what I currently have:

public BinarySearchTree<E> rcopy(){
   BinarySearchTree newTree = new BinarySearchTree();
   newTree.add(rcopy(root).element);
   return newTree;
}


private Entry <E> rcopy(Entry <E> current){
   if(current.left!=null) return rcopy(current.left);
   if(current.right!=null) return rcopy(current.right);
   return current;
}

And here is Entry class so you know what I have available to me:

protected static class Entry<E> {
    protected E element;
    protected Entry<E> left = null,
                       right = null,
                       parent;
    protected int  pos;
protected Entry<E> link = null;
public Entry() { }
    public Entry (E element, Entry<E> parent) 
{
       this.element = element;
       this.parent = parent;
    }
}

Answer 1

private Entry <E> rcopy(Entry <E> current){
   if(current.left!=null) return rcopy(current.left);
   if(current.right!=null) return rcopy(current.right);
   return current;
}

This will not copy anything. It will return the left-most ( or right-most, if no left child; or current, if it is a leaf node ) child of the current node. Because you always return current. You need somelthing like:

private Entry <E> rcopy(Entry <E> current){
    if (current == null) return null;
    return new Entry <E> (current.element, rcopy(current.left), rcopy(current.right)); //write a constructor for that
 }

and actually copy the nodes. I haven't tested the code and it is bit late, hope it is still correct.

Is there a reason you distinguish between BinarySearchTree<E> and Entry<E> ? Isn't a part of the tree also a tree?

Answer 2

Just thought I would share the solution that I got. My main problem was not doing a deep copy on the object so, it would reference the object instead of creating a new one.

public BinarySearchTree<E> rcopy(){
   BinarySearchTree<E> newTree = new BinarySearchTree<E>();
   newTree.root = rcopy(root);
   newTree.size=newTree.nodes();
   return newTree;
}
private Entry <E> rcopy(Entry <E> current){
   Entry <E> b=new Entry<E>();
   if(current!=null){
      if(current.left!=null)b.left=rcopy(current.left);
      if(current.right!=null)b.right=rcopy(current.right);
      b.element = current.element;
      b.parent = successor(current);
   }
   return b;
}

(successor is a method that returns an entry of the object that preceeds it) Thank you every one for help with the problem!