static boolean hasCycle(SinglyLinkedListNode head) {
        Set<SinglyLinkedListNode> nodeSet = new HashSet<>();
        SinglyLinkedListNode node = head;
        while (node != null) {
            if (nodeSet.contains(node)) {
                return true;
            }
            nodeSet.add(node);
            node = node.next;
        }
        return false;
    }