466. 链表节点计数 

计算链表中有多少个节点.

 

样例

给出 1->3->5, 返回 3.

1 /** 2  * Definition of ListNode 3  * class ListNode { 4  * public: 5  *     int val; 6  *     ListNode *next; 7  *     ListNode(int val) { 8  *         this->val = val; 9  *         this->next = NULL;10  *     }11  * }12  */13 14 15 class Solution {16 public:17     /*18      * @param head: the first node of linked list.19      * @return: An integer20      */21     int countNodes(ListNode * head) {22         // write your code here23         int count = 0;24         while (head->next) {25             count++;26             head = head->next;27         }28         return count;29     }30 };