Linked List Cycle

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