java实现中奖概率

1. 算法分析根据概率将奖品划分区间，每个区间代表一个奖品，然后抽取??随机数??，反查落在那个区间上，即为所抽取的奖品。

代码核心算法import com.alibaba.fastjson.JSONObject;import java.math.BigDecimal;import java.util.*;//抽奖核心算法public class Arithmetic { // 放大倍数 private static final int mulriple = 1000000; public static int pay(List<Prize> prizes) { int lastScope = 0; // 洗牌，打乱奖品次序 Collections.shuffle(prizes); Map prizeScopes = new HashMap(); Map prizeQuantity = new HashMap(); for (Prize prize : prizes) { int prizeId = prize.getPrizeId(); // 划分区间 int currentScope = lastScope + prize.getProbability().multiply(new BigDecimal(mulriple)).intValue(); prizeScopes.put(prizeId, new int[]{lastScope + 1, currentScope}); prizeQuantity.put(prizeId, prize.getQuantity()); lastScope = currentScope; } // 获取1-1000000之间的一个随机数 int luckyNumber = new Random().nextInt(mulriple); int luckyPrizeId = 0; // 查找随机数所在的区间 if ((null != prizeScopes) && !prizeScopes.isEmpty()) { Set set = prizeScopes.entrySet(); for (Object o : set) { Map.Entry m = (Map.Entry) o; int key = (int) m.getKey(); Object value = m.getValue(); Integer[] val = JSONObject.parseObject(JSONObject.toJSONString(value), Integer[].class); if (luckyNumber >= val[0] && luckyNumber <=val[1] && Integer.parseInt(prizeQuantity.get(key)+””) > 0) { luckyPrizeId = key; break; } } }// if (luckyPrizeId > 0) {// // 奖品库存减一// } return luckyPrizeId; } public static void main(String[] args) { List<Prize> prizes = new ArrayList(); Prize prize1 = new Prize(); prize1.setPrizeId(10000); prize1.setProbability(new BigDecimal(0.01)); prize1.setQuantity(1); prizes.add(prize1); Prize prize2 = new Prize(); prize2.setPrizeId(10001); prize2.setProbability(new BigDecimal(0.19)); prize2.setQuantity(10); prizes.add(prize2); Prize prize3 = new Prize(); prize3.setPrizeId(10); prize3.setProbability(new BigDecimal(0.8)); prize3.setQuantity(1); prizes.add(prize3); int times = 1000; int prize1GetTimes = 0; int prize2GetTimes = 0; int prize3GetTimes = 0; for (int i = 0; i < times; i++) { int pay = pay(prizes); System.out.println(“抽奖到了”+pay); switch (pay) { case 10000: prize1GetTimes++; break; case 10001: prize2GetTimes++; break; case 10: prize3GetTimes++; break; } } System.out.println(“抽奖次数” + times); System.out.println(“prize1中奖次数” + prize1GetTimes); System.out.println(“prize2中奖次数” + prize2GetTimes); System.out.println(“prize3中奖次数” + prize3GetTimes); }}

3、抽奖对象

import lombok.Data;import java.math.BigDecimal;@Datapublic class Prize { //奖品唯一标示 private Integer prizeId; //中奖概率 private BigDecimal probability; //奖品数量 private Integer quantity;}

执行结果如下：

通过1000次抽取，我们看出算法精度还是很高的。

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