翻转链表

    public ListNode reverseList(ListNode head) {
        if(head==null || head.next ==null){
            return head;
        }
        ListNode cur = head.next;
        head.next = null;
        while(cur!=null){
            ListNode tmp = cur.next;//保留后面的链表头
            //处理当前结点
            cur.next = head;
            head = cur;
            cur = tmp;  
        }
        return head;
    }