万恶之源-链表反转

 //链表反转
    public ListNode reverseList(ListNode head){
        ListNode pre = null;
        ListNode next = null;
        while (head != null) {
            next = head.next;
            head.next = pre;
            pre = head;
            head = next;
            count+=1;
        }
        return pre;
    }

贴代码：三指针法

 

 

方法二：

头插法！！！自行思考