题解 | #判断链表中是否有环#
判断链表中是否有环
http://www.nowcoder.com/practice/650474f313294468a4ded3ce0f7898b9
使用快慢指针，slow和quick，一个走一步，一个走两步，有环必定会相遇，注意判空
/**
* 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) {
if (null == head || head.next == null) {
return false;
}
ListNode slow = head;
ListNode quick = head;
while (null != slow && null != quick) {
slow = slow.next;
if (null != quick.next) {
quick = quick.next.next;
if (null != slow && slow == quick) {
return true;
}
}
}
return false;
}
}
