判断单链表有闭环

class Node
{
    public int Value { get; set; }

    public Node Next { get; set; }
}

public bool IsCricle(Node node)
{
    Node fast = node;
    Node slow = node;
    while (node.Next != null)
    {
        slow = slow.Next;
        fast = fast.Next;
        if (fast != null && fast.Next != null)
            fast = fast.Next;
        else
            return false;
        node = node.Next;
        if (fast == slow)
            return true;
    }
    return false;
}