快慢指针算法-判断单向链表是否有环

判断单链表是否有环，如果有环的话，具体再有环的节点是哪个？

    static class Node {
        private Node next;
        private int val;

        public Node(Node next, int val) {
            this.next = next;
            this.val = val;
        }

        public Node getNext() {
            return next;
        }

        public void setNext(Node next) {
            this.next = next;
        }

        public int getVal() {
            return val;
        }

        public void setVal(int val) {
            this.val = val;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Node node = (Node) o;
            return val == node.val &&
                    Objects.equals(next, node.next);
        }
    }

    public static void main(String[] args) {
        Node node1 = new Node(null, 1);
        Node node2 = new Node(node1, 2);
        Node node3 = new Node(node2, 3);
        Node node4 = new Node(node3, 4);
        Node node5 = new Node(node4, 5);
        Node node6 = new Node(node5, 6);
        Node node7 = new Node(node6, 7);
        Node node8 = new Node(node7, 8);
        Node tail = new Node(node8, 9);
        node1.setNext(node4);

        Node slow = tail;
        Node fast = tail;
        int count = 1;
        slow = slow.next;
        fast = fast.next.next;
        while (slow.val != fast.val) {
            count++;
            slow = slow.next;
            fast = fast.next.next;
        }

        System.out.println(JSON.toJSONString(slow.val) + ";count=" + count);
        slow = tail;
        slow = slow.next;
        fast = fast.next;
        while (slow.val != fast.val) {
            slow = slow.next;
            fast = fast.next;
        }
        System.out.println(JSON.toJSONString(slow.val));
    }