public Node toBalancedBST(Node head){
        LinkList ll = new LinkList();
        int size = ll.size(head);
        NodeRef headRef = new NodeRef();
        headRef.node = head;
        return toBalancedBST(headRef, size);
    }
http://www.geeksforgeeks.org/sorted-linked-list-to-balanced-bst/
Test cases
empty list
0 1 or more node lists
src/com/interview/linklist/SortedLLToBalancedBST.java