package problems;

public class LeetCode142 {
    public ListNode detectCycle(ListNode head) {
        ListNode fast = head, slow = head;
        while (true) {
            if(fast == null || fast.next == null) {
                return null;
            }
            fast = fast.next.next;
            slow = slow.next;
            if(fast == slow) break;
        }
        fast = head;
        while (slow != fast) {
            slow = slow.next;
            fast = fast.next;
        }
        return fast;
    }
}

class LeetCode142_1{
    public ListNode detectCycle(ListNode head) {
        return null;
    }
}