leetcode

0 class Solution {

1 public:

2 ListNode *detectCycle(ListNode *head) {

3 if (!head) return nullptr;

4

5 ListNode *slow, *fast;

6 fast = slow = head;

7 while (fast->next && fast->next->next) {

8 fast = fast->next->next;

9 slow = slow->next;

10 if (fast == slow) {

11 fast = head;

12 while (fast != slow) {

13 fast = fast->next;

14 slow = slow->next;

15 }

16 return slow;

17 }

18 }

19 return nullptr;

20 }

21 };