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;

@Data
public 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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