public void print(Node root){
        Node curr = null;
        while(root != null){
            curr = root;
            System.out.print(root.data + " ");
            root = root.right;
        }
        System.out.println();
        root = curr;
        while(root != null){
            System.out.print(root.data + " ");
            root = root.left;
        }
    }
http://www.geeksforgeeks.org/convert-given-binary-tree-doubly-linked-list-set-3/
src/com/interview/tree/BinaryTreeToDoubleLinkList.java