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public class LinkedListCycleII {
public ListNode detectCycle(ListNode head) {
if (head == null || head.next == null) {
return null;
}
ListNode fast = head.next.next;
ListNode slow = head.next;
while (fast != null && fast != slow) {
slow = slow.next;
fast = fast.next != null ? fast.next.next : null;
}
if (fast == null) {
return null;
}
fast = head;
while (fast != slow) {
fast = fast.next;
slow = slow.next;
}
return fast;
}
}
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