一個C#隨機數的問題，解決隨機數重複

預設情況下，.NET的隨機數是根據系統時間來產生的，如果電腦速度很快的話，產生的隨機數就會一樣。
Random rnd = new Random();
int rndNum = rnd.Next();         //int 取值範圍內的隨機數
int rndNum = rnd.Next(10);       //得0~9的隨機數
int rndNum = rnd.Next(10,20);    //得10~19的隨機數
int rndNum = rnd.NextDouble();   //得0~1的隨機數   若隨機種子為系統時間,用迴圈一次產生多個隨機數.
因為CPU運算速度太快了,所以每次取到的都是同一個時間.即產生的數字都一樣了.
所以要不停地變換種子.        public string GetRandomCode()
         {
             char[] chars = {
                                'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'M', 'N', 'P', 'Q', 'R', 'S',
                                'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '2', '3', '4', '5', '6', '7', '8', '9'
                            };

             string code = string.Empty;

             for (int i = 0; i < 4; i++)
             {

                 //這裡是關鍵，傳入一個seed參數即可保證產生的隨機數不同            
                 //Random rnd = new Random(unchecked((int)DateTime.Now.Ticks));
                 Random rnd = new
Random(GetRandomSeed( ));
                 code += chars[rnd.Next(0, 30)].ToString();
             }

             return code;
         }

        /// <summary>
        /// 加密隨機數產生器 產生隨機種子
        /// </summary>
        /// <returns></returns>

    staticint GetRandomSeed()

    {

        byte[] bytes =
newbyte[4];

        System.Security.Cryptography.RNGCryptoServiceProvider rng = new System.Security.Cryptography.RNGCryptoServiceProvider();

        rng.GetBytes(bytes);

        returnBitConverter.ToInt32(bytes, 0);

    }

擷取指定數量的隨機組合 洗牌程式 思路

    public static IList<string> CreateChargeCodeNo(string PromotionChargeCodeNo, int Count)

    {

        List<string> lis = new List<string>();

        if (string.IsNullOrEmpty(PromotionChargeCodeNo))

        {

            return lis;

        }

        string ChargeCodeNo = PromotionChargeCodeNo;

        int length = 10 - PromotionChargeCodeNo.Length;

        while (lis.Count < Count)

        {

            int[] numbers = new int[length * 2];

            for (int i = 0; i < length * 2; i++)

                numbers[i] = i + 1;

            for (int i = 0; i < length * 2; i++)//二倍體洗牌

            {

                Random rand = new Random(GetRandomSeed());

                int temp = rand.Next(length * 2);

                int tempNumber = numbers[i];

                numbers[i] = numbers[temp];

                numbers[temp] = tempNumber;

            }

            string code = "";

            for (int x = 0; code.Length < length; x++)

            {

                code += numbers[x];

            }

            code = code.Substring(0, length);

            string s = ChargeCodeNo + code;

            if (lis.Contains(s))

            {

                continue;

            }

            lis.Add(ChargeCodeNo + code);

        }

        return lis;

    }