141. Linked List Cycle

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： http://leetcode.com/problems/linked-list-cycle/

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 }