算法2：链表的中间结点

题目链接

解析：

完整代码：

typedef struct ListNode ListNode;
class Solution {
public:
    ListNode* middleNode(ListNode* head) {
    ListNode*slow,*fast;
    slow = fast = head;
    while(fast && fast->next)
    {
        slow = slow -> next;
        fast = fast -> next -> next;
    }
    return slow;
    }
};