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不确定人数的抽奖方法
很多年前就给前公司的年会做过年会抽奖,基本要求就是年会入场时签到,签到的员工都参与抽奖(也可以设置公司高管过滤,不参与抽奖),奖品是预设好的,到时候就是给所有签到员工编号,然后抽奖过程中不断生成一组随机数,这些随机数对应的编号的员工姓名和照片就显示出来,这是很容易想到的算法。
但是还要一种情况就是互联网模式的抽奖,有点像双十一之前,阿里派发红包一样,大家都可以在开始抽奖的时候去抽,奖品也是预设好的,比如1000W的奖金池,派发完毕就抽奖完毕,每个用户可以抽取多次。这种抽奖方式主要是应对抽奖人数不确定的情况,谁也不需要提前签到报名,到了抽奖时间只要注册用户都可以抽奖。
因为抽奖人数不确定,所以采用一人多次抽奖的方案是很好的,对用户来说也是,如果第一次没有抽中,还可以尝试第二次,第三次。具体算法上,其实更简单,因为用户点击抽奖的顺序是随机的,所以我们连随机数都不用用,直接给用户的一次抽奖请求编个自增的号,如果这个号满足中奖规则,那么就分配礼品,返回该抽奖请求中奖结果,如果不满足中奖规则,那么我们就返回未中奖。
为了避免用户频繁的点击,造成服务器过高的负担,我们可以在客户端设置一个动画过程,比如转盘抽奖,可以转几秒以后才请求服务器,看是否中奖,对用户来说也增加了趣味性。为了避免用户不通过客户端,直接发起频繁的HTTP请求来刷奖,我们甚至可以在服务器设置同一个用户的请求时间间隔。
下面贴出我写的一个示例代码部分,我设置了一个自增的整数Sequence ,每个正常的抽奖请求,则Sequence ++,另外设置默认的抽奖基数baseNumber=100,如果能够Sequence能够被baseNumber整除,那么就中奖,否则不中奖:
[RoutePrefix("api/Lottery")] public class LotteryController : AbpApiController { private static volatile int Sequence = 1; private static IList<int> winnerList=new List<int>(); /// <summary> /// 抽奖开始标记,请通过StartNewLotteryRound打开 /// </summary> private static bool start = false; /// <summary> /// 所有产品都被抽完了的标记 /// </summary> private static bool allPrizeOut = false; /// <summary> /// 当前轮次ID /// </summary> private static int currentRoundId = 0; public ILotteryAppService LotteryAppService { get; set; } /// <summary> /// 抽奖基数,只要被该数整除就中奖 /// </summary> private static int baseNumber =100; private static IDictionary<int,DateTime> userDrawTime=new Dictionary<int, DateTime>(); private bool CheckUserDrawTime(int userId) { if (userDrawTime.ContainsKey(userId)) { return userDrawTime[userId].AddSeconds(8) < DateTime.Now;//8s后可以抽奖 } else { return true; } } /// <summary> /// 抽奖一次 /// </summary> /// <param name="userId"></param> /// <returns></returns> [HttpGet] [Route("Draw/{userId}")] public DrawResult Draw(int userId) { if (!start) { return new DrawResult(400,0, "抽奖未开始"); } if (allPrizeOut) { return new DrawResult(400, 0, "所有奖品已抽完"); } if (!CheckUserDrawTime(userId)) { return new DrawResult(400, 0, "请求过于频繁,请稍后再试"); } int myNumber = Sequence++; userDrawTime[userId] = DateTime.Now;//记录用户这次抽奖的时间 if (myNumber%baseNumber == 0) //中奖啦! { if (winnerList.Contains(userId)) { //用户已经中奖,不用再抽 return new DrawResult(200, 0, "您已经中过奖了"); } var result = LotteryAppService.WriteAWinner(userId, currentRoundId); switch (result.ExceptionType) { case LotteryExceptionType.NoException: { winnerList.Add(userId); return new DrawResult(200, result.PrizeId, ""); } case LotteryExceptionType.AllPrizeOut: { allPrizeOut = true; return new DrawResult(400, 0, "所有奖品已抽完"); } case LotteryExceptionType.InvalidLotteryRound: { return new DrawResult(400, 0, "抽奖轮次无效"); } default: { return new DrawResult(400, 0, "当前用户无效"); } } } return new DrawResult(200, 0, ""); } /// <summary> /// 获得我的奖品对象 /// </summary> /// <param name="userId"></param> /// <returns></returns> [HttpGet] [Route("MyPrize/{userId}")] public IList<LotteryDto> GetMyPrize(int userId) { return LotteryAppService.GetMyPrize(userId); } /// <summary> /// 开始新一轮的抽奖 /// </summary> /// <param name="roundId"></param> [HttpPost] [Route("StartNewLotteryRound")] [AbpApiAuthorize(PermissionNames.Admin)] public bool StartNewLotteryRound(int roundId) { start = true; allPrizeOut = false; currentRoundId = roundId; return true; } /// <summary> /// 获得当前轮次的奖品和获奖者 /// </summary> /// <returns></returns> [HttpGet] [Route("")] public IList<LotteryDto> GetLotteries() { return LotteryAppService.GetLotteries(currentRoundId); } /// <summary> /// 获得所有的奖品和获奖者 /// </summary> /// <returns></returns> [HttpGet] [Route("All")] public IList<LotteryDto> GetAllLotteries() { return LotteryAppService.GetLotteries(0); } /// <summary> /// 清空中奖结果,各种缓存 /// </summary> /// <returns></returns> [HttpPost] [Route("Clean")] [AbpApiAuthorize(PermissionNames.Admin)] public bool Clean() { Sequence = 1; start = false; winnerList.Clear(); LotteryAppService.CleanLotteries(); return true; } /// <summary> /// 获取是否显示抽奖图标 /// </summary> /// <returns></returns> [HttpGet] [Route("ShowLotteryIcon")] public bool GetShowLotteryIcon() { return LotteryAppService.ShowLotteryIcon; } /// <summary> /// 设置是否显示抽奖图标 /// </summary> /// <param name="show"></param> /// <returns></returns> [HttpPut] [Route("ShowLotteryIcon/{show}")] public HttpResponseMessage SetShowLotteryIcon(bool show) { try { LotteryAppService.ShowLotteryIcon = show; return Request.CreateResponse(HttpStatusCode.OK, true); } catch (Exception ex) { var resp = new HttpResponseMessage(HttpStatusCode.BadGateway) { Content = new StringContent("设置ShowLotteryIcon失败:" + ex.Message), ReasonPhrase = "Gateway failed" }; throw new HttpResponseException(resp); } } /// <summary> /// 设置Base Number /// </summary> /// <param name="number"></param> /// <returns></returns> [HttpPut] [AbpApiAuthorize(PermissionNames.Admin)] [Route("SetBaseNumber/{number}")] public bool SetBaseNumber(int number) { baseNumber = number; return true; } }
不确定人数的抽奖方法