Linked List Cycle

 1 public class Solution {
 2     public boolean hasCycle(ListNode head) {
 3         if(head==null) return false;
 4         ListNode fast = head;
 5         ListNode slow = head;
 6         while(fast!=null){
 7             slow = slow.next;
 8             fast = fast.next;
 9             if(fast==null)
10                 return false;
11             fast = fast.next;
12             if(fast==slow) return true;
13         }
14         return false;
15     }
16 }