109. Convert Sorted List to Binary Search Tree

class Solution {
    ListNode lnode=null;
    public TreeNode sortedListToBST(ListNode head) {
        int size=0;
        ListNode p=head;
        while(p!=null)
        {
            p=p.next;
            size++;
        }
        lnode=head;
        return buildBST(size);
    }
    private TreeNode buildBST(int size){
        if(size==0)
            return null;
        TreeNode tnode=new TreeNode(0);
        tnode.left=buildBST(size/2);
        tnode.val=lnode.val;
        lnode=lnode.next;
        tnode.right=buildBST(size-size/2-1);
        return tnode;
    }
}