public TreeNode sortedListToBST(ListNode head) {

        ArrayList<Integer> list=new ArrayList<Integer>();

        while(head!=null){

        	list.add(head.val);

        	head=head.next;

        }

        return sortedListToBST(list,0,list.size()-1);

    }

	static public TreeNode sortedListToBST(ArrayList<Integer> list, int begin, int end) {

		if (begin>end)

			return null;

		TreeNode root = new TreeNode(list.get((begin+end) / 2));

		root.left=sortedListToBST(list,begin,(begin+end) / 2-1);

		root.right=sortedListToBST(list,(begin+end) / 2+1,end);

		return root;

	}