private static ListNode reverseOrder(ListNode head){
	    	if(head == null || head.next ==null) return head;
	    	
	    	ListNode pre = head;
	    	ListNode current = head.next;
	    	
	    	while(current!=null){
	    		ListNode temp = current.next;
	    		current.next = pre;
	    		pre = current;
	    		current = temp;
	    	}
	    	
	    	head.next = null;
	    	return pre;
	    }