[Unity菜鸟] 产生各不相同的随机数

Random r = new Random(DateTime.Now.Millisecond);

Random Counter = new Random(unchecked((int)(DateTime.Now.Ticks >> ctr)));

Random Counter = new Random(System.Guid.NewGuid().GetHashCode());

string testStr;
    void OnGUI()
    {
        if (GUILayout.Button("产生随机数"))
        {
            testStr = "";

            Hashtable hashtable = new Hashtable();
            System.Random rm = new System.Random();
            int RmNum = 3;
            for (int i = 0; hashtable.Count < RmNum; i++)
            { 
                int nValue = rm.Next(3);
                if (!hashtable.ContainsValue(nValue))
                {
                    hashtable.Add(nValue, nValue);    //Add(key,value)
                    testStr += nValue + " ";
                }
            }
        }
        GUILayout.Label(testStr);
    }