题目:

Given a linked list, determine if it has a cycle in it.

Follow up:

Can you solve it without using extra space?

链接： 

2/18/2017, Java

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