Linked List Cycle

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?

这道题要用双指针，但我想试一下投机取巧的办法行不行，果然A了

 1 /**
 2  * Definition for singly-linked list.
 3  * class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     public boolean hasCycle(ListNode head) {
14         if(null == head)
15             return false;
16         ListNode point = head;
17         while(null != point){
18             if(point.val != Integer.MIN_VALUE)
19                 point.val = Integer.MIN_VALUE;
20             else
21                 return true;
22                 point = point.next;
23         }        
24         return false;
25     }
26 }

 双指针，一个走一步一个走两步，有环两个一定会相遇

 1 /**
 2  * Definition for singly-linked list.
 3  * class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     public boolean hasCycle(ListNode head) {
14         if(null == head)
15             return false;
16         ListNode slow = head;
17         ListNode fast = head;
18         while(fast != null && fast.next != null){
19             slow = slow.next;
20             fast = fast.next.next;
21             if(slow == fast)
22                 return true;
23         }
24         return false;
25     }
26 }

 

posted on 2014-11-20 19:56  luckygxf  阅读(130)  评论(0)  编辑  收藏  举报

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