Grokking 222

public ListNode detectCycle(ListNode head) {
    ListNode fast = head;
    ListNode slow = head;
    ListNode temp = head;
    while(fast != null && fast.next != null) {
        slow = slow.next;
        fast = fast.next.next;

        if (fast == slow) {
            while(temp != slow) {
                temp = temp.next;
                slow = slow.next;
            }
            return temp;
        }
    }

    return null;
}