java实现中奖概率

Posted 2022-07-13 码农小宋

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。

2. 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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