题目： 

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解析： 

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也可以把链表看作一棵树，后续遍历这棵树然后和上图一样，改变指针即可 

代码： 

public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null) return head;
        ListNode newHead = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newHead;
    }