```
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
bool hasCycle(ListNode *head) {
if(head==NULL || head->next==NULL)
return false;
ListNode* fast = head->next->next;
ListNode* slow = head->next;
while(fast && fast->next)
{
if(fast==slow)
return true;
else
{
fast = fast->next->next;
slow = slow->next;
}
}
return false;
}
};
```