[数据结构与算法]判断链表是否有环（简单）

public class Solution {
    public boolean hasCycle(ListNode head) {
        if (head == null || head.next == null) {
            return false;
        }
        ListNode slow = head;
        ListNode fast = head.next;
        while (slow != fast) {
            if (fast == null || fast.next == null) {
                return false;
            }
            slow = slow.next;
            fast = fast.next.next;
        }
        return true;
    }
}

用do-while循环坐

public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head==null||head.next==null) return false;
        ListNode last=head,fast=head;
        do{
            if(fast==null||fast.next==null) return false;
            fast=fast.next.next;
            l=last.next;


        }while(fast!=last);
        return true;
       
    }
}