CODE 138. Linked List Cycle

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/11/24/2013-11-24-CODE 138 Linked List Cycle/

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Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?

public boolean hasCycle(ListNode head) {
     // IMPORTANT: Please reset any member data you declared, as
     // the same Solution instance will be reused for each test case.
     if(null == head){
         return false;
     }
 	ListNode first = head;
 	ListNode second = head;
 	while(first.next != null && first.next.next !=null){
 		if(first.next.equals(second) || first.next.next.equals(second)){
 			return true;
 		}
 		first = first.next.next;
 		second = second.next;
 	}
 	if(first.next != null && first.next.equals(second)){
 		return true;
 	}
 	return false;
 }