* 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(head == null || head.next == null){
return false;
}
//快慢指针 相遇则有环
ListNode fast = head;
ListNode slow = head;
while(fast != null && slow != null){
fast = fast.next;
if(fast != null){
fast = fast.next;
}
slow = slow.next;
if(fast == slow){
return true;
}
}
return false;
}
}