【leetcode刷题笔记】Linked List Cycle

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

Follow up:
Can you solve it without using extra space?

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题解：参见http://www.cnblogs.com/sunshineatnoon/p/3825032.html

代码如下：

 /**
  * 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 p1 = head;
         ListNode p2 = head;

         while(p2 != null){
             p1 = p1.next;
             p2 = p2.next;
             if(p2 != null)
                 p2 = p2.next;
             else
                 return false;
             if(p1 == p2)
                 return true;
         }
         return false;
     }
 }