题目：从尾到头打印链表

介绍：输入一个链表，按链表从尾到头的顺序返回一个ArrayList
思路：链表原地置换

 public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> result = new ArrayList<>();
        if (listNode == null) {
            return result;
        }
        ListNode current = listNode; //当前节点
        ListNode next = current.next; //下一个节点
        listNode = null; //头结点置空
        while (current != null) {
            current.next = listNode; //当前节点指向头结点
            listNode = current; // 头结点改为当前结点
            //继续往后走
            current = next;
            if (current != null) {
                next = current.next;
            }
        }
        while (listNode != null) {
            result.add(listNode.val);
            listNode = listNode.next;
        }
        return result;
    }