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){//这里注意空指针异常
return false;
}
slow=slow.next;
fast=fast.next.next;
}
return true;
}
}
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