环形链表
解法一:Set去重
import java.util.HashSet;
import java.util.Set;
public class LeetCode_141 {
public static boolean hasCycle(ListNode head) {
if (head == null || head.next == null) {
return false;
}
Set<ListNode> appeared = new HashSet<>();
while (head != null) {
if (!appeared.add(head)) {
return true;
}
head = head.next;
}
return false;
}
public static void main(String[] args) {
ListNode head = new ListNode(1);
head.next = new ListNode(2);
System.out.println(hasCycle(head));
}
}