142. Linked List Cycle II

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.

此题和之前的find the duplicate number比较像，代码如下：

 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 ListNode detectCycle(ListNode head) {
14         ListNode fast = head;
15         ListNode slow = head;
16         while(fast!=null&&fast.next!=null){
17             fast = fast.next.next;
18             slow = slow.next;
19             if(fast==slow){
20                 fast = head;
21                 while(fast!=slow){
22                     fast = fast.next;
23                     slow = slow.next;
24                 }
25                 return fast;
26             }
27         }
28         return null;
29     }
30 }

 

posted @ 2017-02-09 07:58  CodesKiller  阅读(110)  评论(0)  编辑  收藏  举报