搞了個抽獎活動，中大獎中的簡直爽歪歪?

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不過還是要偷偷告訴你：抽獎是有內幕的~~~（不能讓領導看到，會被打?）

總在各種app上看到轉盤抽獎，翻牌抽獎，每次抱著中最大獎的心，換來的都是未中獎的提示，可謂是竹籃打水一場空，屢戰屢敗，屢敗屢戰~

現在就聊聊中獎的事，搬好小板凳排隊做好了??♂????♂????♂?????????????

一、實現思路（這個應該不難理解吧~）

每個獎品都有對應的中獎概率，先對所有獎品中獎概率求和
計算出每個獎品在0-1之間所占的區間塊
隨機產生0-1之間的隨機數，隨機數落在哪個區間，就是中獎哪個?
例如現有以下獎品：?
獎品A 中獎概率為 0.1?
獎品B 中獎概率為 0.01?
獎品C 中獎概率為 0.001?
獎品D 中獎概率為 0.8

第一步：求出概率總和 0.1+0.01+0.001+0.8 = 0.911?
第二步：計算每個獎品的所占區間塊?
獎品A： 0.1 / 0.911 = 0.1098?
獎品B： （0.1+0.01）/ 0.911 = 0.1207?
獎品C：（0.1+0.11+0.001）/ 0.911 = 0.1218?
獎品D：（0.1+0.11+0.001+0.8）/ 0.911 = 1?
則：?
獎品A的所占區間為：0~0.1098?
獎品B的所占區間為：0.1098~0.1207?
獎品C的所占區間為：0.1207~0.1218?
獎品D的所占區間為：0.1218~1
到此為止思路應該了解了，不過我要做的是這個的升級版

根據不同類型的人分別設置概率（emm~換句話說根據身份設置概率發放獎品）

特此說明一下：里面的概率10代表10%，可以精確到小數點后兩位，比如 0.01%

二、干貨如下

import lombok.Data; import lombok.ToString; /*** @Author: yansf* @Description:獎勵實體* @Date:Creat in 10:35 AM 2019/1/16* @Modified By:*/ @Data @ToString public class RewardDto {/*** 獎品id*/private int welfareId;/*** 天天福利管理Id(Welfare_ManagerId)*/private int welfareMgrId;/*** 獎品名稱*/private String welfareName;/*** 獎品類型(游戲幣10 vip試用20 京東卡30)*/private int welfareType;/*** 獎品數量（單個獎品上限）*/private int AwardCount;/*** 獎品值*/private int welfareValue;/*** 獎品概率 (10代表10%)*/private int AwardPct;/*** 子概率-A類概率*/private int APct;/*** 子概率-B類概率*/private int BPct;/*** 子概率-C類概率*/private int CPct;/*** 子概率-D類概率*/private int DPct;/*** 獎品剩余庫存*/private int remainderAmount;/*** 獎品配置庫存*/private int totalAmount;} /*** @Author: yansf* @Description:userType 1-A類人 2-B 5-C 7-D* @Date: 11:28 AM 2019/9/5* @Modified By:*/public RewardDto lottery1(int userId, boolean isVip, int userType) {RewardDto dto = null;RewardDto dto1 = null;//獲取獎品配置信息List<RewardDto> list = welfareMapper.getRewardPctList();if (dto == null) {OptionalInt s = list.stream().filter(e -> e.getWelfareType() == 10).mapToInt(RewardDto::getWelfareValue).min();dto1 = list.stream().filter(e -> e.getWelfareValue() == s.getAsInt()).findAny().orElse(null);}//移除庫存為0的獎品list.removeIf(e -> e.getRemainderAmount() == 0);var firstReward = welfareMapper.getWelfareReceiveRecord(userId, null, null);//近一個月內是否中獎過vip試用，不再抽中vipvar vipTrial = welfareMapper.getvipTrialRecord(userId);//如果已經是vip，則不可抽vipif (isVip || vipTrial > 0) {list.removeIf(e -> e.getWelfareType() == 20);}//如果活動間第一次抽獎，中最小的獎的概率為0if (firstReward <= 0 && (list.size() >= 2)) {//移除最小獎的配置OptionalInt s = list.stream().filter(e -> e.getWelfareType() == 10).mapToInt(RewardDto::getWelfareValue).min();list.removeIf(e -> e.getWelfareValue() == s.getAsInt() && e.getWelfareType() == 10);}if (list != null && list.size() > 0) {//總的概率區間float totalPro = 0f;//存儲每個獎品新的概率區間List<Float> proSection = new ArrayList<Float>();DecimalFormat df = new DecimalFormat("######0.00");int random = -1;try {//計算總權重double sumWeight = 0;for (RewardDto award : list) {if (userType == 1) {sumWeight += award.getAPct();} else if (userType == 2) {sumWeight += award.getBPct();} else if (userType == 5) {sumWeight += award.getCPct();} else if (userType == 7) {sumWeight += award.getDPct();}}//產生隨機數double randomNumber;randomNumber = Math.random();//根據隨機數在所有獎品分布的區域并確定所抽獎品double d1 = 0;double d2 = 0;for (int i = 0; i < list.size(); i++) {if (userType == 1) {d2 += Double.parseDouble(String.valueOf(list.get(i).getAPct())) / sumWeight;if (i == 0) {d1 = 0;} else {d1 += Double.parseDouble(String.valueOf(list.get(i - 1).getAPct())) / sumWeight;}} else if (userType == 2) {d2 += Double.parseDouble(String.valueOf(list.get(i).getBPct())) / sumWeight;if (i == 0) {d1 = 0;} else {d1 += Double.parseDouble(String.valueOf(list.get(i - 1).getBPct())) / sumWeight;}} else if (userType == 5) {d2 += Double.parseDouble(String.valueOf(list.get(i).getCPct())) / sumWeight;if (i == 0) {d1 = 0;} else {d1 += Double.parseDouble(String.valueOf(list.get(i - 1).getCPct())) / sumWeight;}} else if (userType == 7) {d2 += Double.parseDouble(String.valueOf(list.get(i).getDPct())) / sumWeight;if (i == 0) {d1 = 0;} else {d1 += Double.parseDouble(String.valueOf(list.get(i - 1).getDPct())) / sumWeight;}}if (randomNumber >= d1 && randomNumber <= d2) {random = i;break;}}} catch (Exception e) {System.out.println("生成抽獎隨機數出錯，出錯原因：" + e.getMessage()); // throw e;}if (random != -1) {dto = list.get(random);}}if (dto == null) {dto = dto1;}return dto;} /*** @Author: yansf* @Description:抽獎測試* @Date: 3:35 PM 2019/8/19* @Modified By:*/@GetMapping(value = "lottery")public ResponseUtil lottery(int userId, boolean isVip, int userType) {int coin = 0;int vip = 0;int jd = 0;RewardDto result = new RewardDto();List<RewardDto> list = new ArrayList();System.out.println("抽獎開始");for (int i = 0; i < 1000; i++) {result = welfareService.lottery(userId, isVip, userType);if (result.getWelfareType() == 10) {coin += 1;} else if (result.getWelfareType() == 20) {vip += 1;} else if (result.getWelfareType() == 30) {jd += 1;}list.add(result);}Map<String, List<RewardDto>> count = list.stream().collect(Collectors.groupingBy(RewardDto::getWelfareName));if (result != null) {return ResponseUtil.response(200, "游戲幣：" + coin + ",vip：" + vip + ",京東卡：" + jd, count);} else {return ResponseUtil.response(500, "未中獎", count);}}

此處循環1000次，使用非vipD類人做一下測試，結果如下圖

概率抽獎其實很簡單，如果又要分獎品概率，又要根據不同人設置不同的概率，那就比重相乘然后相加，舉個簡單的例子：

//計算總權重double sumWeight = 0;for (RewardDto award : list) {if (userType == 1) {//此處獎品概率*不同人抽到該獎品的概率sumWeight += award.getAPct()*avard.getPct();} } for (int i = 0; i < list.size(); i++) {if (userType == 1) { //概率相乘d2 += Double.parseDouble(String.valueOf(list.get(i).getAPct()*list.get(i).getPct())) / sumWeight;if (i == 0) {d1 = 0;} else {d1 += Double.parseDouble(String.valueOf(list.get(i - 1).getAPct()*list.get(i).getPct())) / sumWeight;}}

看到這，你應該學會了吧???

（不得不diss下，多數抽獎活動大獎概率設置的很低甚至為0，大獎可謂是可望不可及，所以還是好好工作比較靠譜，寫bug，找bug，改bug? ? ???emm~）

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