抽奖算法

/// <summary>
/// 抽奖
/// </summary>
public class Prize
{
    /// <summary>
    /// 奖品关键字
    /// </summary>
    public string Key { get; set; }

    /// <summary>
    /// 权重/数量
    /// </summary>
    public int Poll { get; set; }


    /// <summary>
    /// 中奖区间
    /// </summary>
    class Area
    {
        /// <summary>
        /// 奖品关键字
        /// </summary>
        public string Key { get; set; }

        /// <summary>
        /// 开始索引位置
        /// </summary>
        public int Start { get; set; }

        /// <summary>
        /// 截止索引位置
        /// </summary>
        public int Over { get; set; }
    }

    /// <summary>
    /// 随机种子
    /// </summary>
    static Random Rand = new Random((int)DateTime.Now.Ticks);


    /// <summary>
    /// 轮盘抽奖，权重值(在轮盘中占的面积大小)为中奖几率
    /// </summary>
    /// <param name="prizeList">礼品列表（如果不是百分百中奖则轮空需要加入到列表里面）</param>
    /// <returns></returns>
    public static string Roulette(List<Prize> prizeList)
    {
        if (prizeList == null || prizeList.Count == 0) return string.Empty;
        if (prizeList.Any(x => x.Poll < 1)) throw new ArgumentOutOfRangeException("poll权重值不能小于1");
        if (prizeList.Count == 1) return prizeList[0].Key; //只有一种礼品

        Int32 total = prizeList.Sum(x => x.Poll); //权重和               
        if (total > 1000) throw new ArgumentOutOfRangeException("poll权重和不能大于1000"); //数组存储空间的限制。最多一千种奖品（及每种奖品的权重值都是1）

        List<int> speed = new List<int>(); //随机种子
        for (int i = 0; i < total; i++) speed.Add(i);

        int pos = 0;
        Dictionary<int, string> box = new Dictionary<int, string>();
        foreach (Prize p in prizeList)
        {
            for (int c = 0; c < p.Poll; c++) //权重越大所占的面积份数就越多
            {
                pos = Prize.Rand.Next(speed.Count); //取随机种子坐标
                box[speed[pos]] = p.Key; //乱序 礼品放入索引是speed[pos]的箱子里面
                speed.RemoveAt(pos); //移除已抽取的箱子索引号
            }
        }
        return box[Prize.Rand.Next(total)];
    }

    /// <summary>
    /// 奖盒抽奖，每个参与者对应一个奖盒，多少人参与就有多少奖盒
    /// </summary>
    /// <param name="prizeList">礼品列表</param>
    /// <param name="peopleCount">参与人数</param>
    /// <returns></returns>
    public static string LunkyBox(List<Prize> prizeList, int peopleCount)
    {
        if (prizeList == null || prizeList.Count == 0) return string.Empty;
        if (prizeList.Any(x => x.Poll < 1)) throw new ArgumentOutOfRangeException("poll礼品数量不能小于1个");
        if (peopleCount < 1) throw new ArgumentOutOfRangeException("参数人数不能小于1人");
        if (prizeList.Count == 1 && peopleCount <= prizeList[0].Poll) return prizeList[0].Key; //只有一种礼品且礼品数量大于等于参与人数

        int pos = 0;
        List<Area> box = new List<Area>();
        foreach (Prize p in prizeList)
        {
            box.Add(new Area() { Key = p.Key, Start = pos, Over = pos + p.Poll }); //把礼品放入奖盒区间
            pos = pos + p.Poll;
        }

        int total = prizeList.Sum(x => x.Poll); //礼品总数
        int speed = Math.Max(total, peopleCount); //取礼品总数和参数总人数中的最大值

        pos = Prize.Rand.Next(speed);
        Area a = box.FirstOrDefault(x => pos >= x.Start && pos < x.Over); //查找索引在奖盒中对应礼品的位置

        return a == null ? string.Empty : a.Key;
    }

}


/*
List<Prize> prizes = new List<Prize>();
prizes.Add(new Prize() { Key = "电脑", Poll = 1 });
prizes.Add(new Prize() { Key = "机柜", Poll = 2 });
prizes.Add(new Prize() { Key = "鼠标", Poll = 3 });
                        

string lp1 = Prize.LunkyBox(prizes, 6);
Console.WriteLine(lp1);


prizes.Add(new Prize() { Key = "谢谢惠顾", Poll = 5 });
string lp2 = Prize.Roulette(prizes);      
Console.WriteLine(lp2);
*/