leetcode--009 Linked List Cycle I

 1 public boolean hasCycle(ListNode head) {
 2         ListNode s=head;
 3         ListNode f=head;
 4         while(f!=null&&f.next!=null){
 5             s=s.next;
 6             f=f.next.next;
 7             if(s==f){
 8                 return true;
 9             }
10         }
11             return false;
12         
13     }