Linked List Cycle

 1 class Solution {
 2 public:
 3     bool hasCycle(ListNode *head) {
 4         struct ListNode *slow = head;
 5         struct ListNode *fast = head;
 6         
 7         while (fast != NULL && fast->next != NULL) {
 8             slow = slow->next;
 9             fast = fast->next->next;
10             
11             if (slow == fast) {
12                 return true;
13             }
14         }
15         return false;
16     }
17 };