生成无重复5位数的邀请码

 staticvoid Main(string[] args)
        {
            int len ="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ".Length -1;
            char[] code ="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray(0, len +1);
            int i =new Random(DateTime.Now.Millisecond).Next(0, len);
            Console.Write(code[i]);
            i =new Random(DateTime.Now.Millisecond*0xFFFF).Next(0, len);
            Console.Write(code[i]);
            i =new Random(DateTime.Now.Millisecond*0xAAAA).Next(0, len);
            Console.Write(code[i]);
            i =new Random(DateTime.Now.Millisecond*0xCCCC).Next(0, len);
            Console.Write(code[i]);
        }