1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     ListNode *next; 6  *     ListNode(int x) : val(x), next(NULL) {} 7  * }; 8  */ 9 class Solution {10 public:11     bool hasCycle(ListNode *head) {12         13         ListNode *fastPoint = head;14         ListNode *slowPoint = head;15         16         if(fastPoint == NULL || fastPoint->next == NULL)17             return false;18             19         while(fastPoint->next != NULL && fastPoint->next->next != NULL)20         {21             fastPoint = fastPoint->next->next;22             slowPoint = slowPoint->next;23             if(fastPoint == slowPoint)24                 return true;25         }26         27         return false;28     }29 };