快速找出长度未知链表的中间节点（快慢指针）

 1 LinkList *GetMidNode(LinkList *head)
 2 {
 3     LinkList *slow = head;
 4     LinkList *fast = slow;
 5     
 6     while(slow)
 7     {
 8         fast = fast->next;
 9         if(fast)
10         {
11             fast = fast->next;
12             slow = slow->next;
13         }
14     }
15     return slow;
16 }