一:题目

二:上码

/*** 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 fast = head;ListNode slow = head;//这里的fast != null 的话就是 我们第一个节点不为空//fast.next.next != null 那么 fast.next 肯定也是 != nullwhile (fast != null && fast.next != null && fast.next.next != null) {fast = fast.next.next;slow = slow.next;if (fast == slow) return true;}return false;}
}