Linked List Cycle

有点取巧，p1 算不算多余的空间？
/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public boolean hasCycle(ListNode head) {
        ListNode p = head;
        ListNode p1 = head;
        while(p!=null&&p1!=null){
            try{
                p=p.next;
                p1 = p1.next.next;
            }catch(Exception e){
                return false;
            }
            if(p==p1){
                return true;
            }
        }
        return false;
    }
}