java 概率抽奖代码实现

package com.sfjiayuan.ld.web.modular.pay;

import com.alibaba.fastjson.JSONObject;
import com.sfjiayuan.ld.web.modular.award.entity.LdDrawAward;

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 LdDrawAward pay(List<LdDrawAward> aWards) {
    int lastScope = 0;
    // 洗牌，打乱奖品次序
    Collections.shuffle(aWards);
    Map<String, int[]> prizeScopes = new HashMap();
    Map<String, LdDrawAward> prizeQuantity = new HashMap();
    for (LdDrawAward award : aWards) {

        String prizeId = award.getId();
        BigDecimal ratio = new BigDecimal(award.getRatio());
        if ((ratio.compareTo(new BigDecimal(0))) > 0) {

            // 划分区间
            int currentScope = lastScope + ratio.multiply(new BigDecimal(mulriple / 100)).intValue();
            prizeScopes.put(prizeId, new int[]{lastScope+1, currentScope});
            prizeQuantity.put(prizeId, award);
            lastScope = currentScope;
        }
    }
    // 获取1-1000000之间的一个随机数
    int luckyNumber = new Random().nextInt(mulriple)+1;
    LdDrawAward luckyResult = null;
    // 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;
            String key = (String) m.getKey();
            Object value = m.getValue();
            Integer[] val = JSONObject.parseObject(JSONObject.toJSONString(value), Integer[].class);
            if (luckyNumber >= val[0] && luckyNumber <= val[1]) {
                luckyResult = prizeQuantity.get(key);
                break;
            }
        }
    }
    if (luckyResult == null) {
        // 奖品库存减一
        System.out.println("--------------   " + luckyNumber);
    }
    return luckyResult;
}

public static void main(String[] args) {
    List<LdDrawAward> prizes = new ArrayList();
    LdDrawAward prize1 = new LdDrawAward();
    prize1.setId("1");
    prize1.setRatio("0.0001");
    prize1.setName("电动车");
    prizes.add(prize1);

    LdDrawAward prize2 = new LdDrawAward();
    prize2.setId("2");
    prize2.setRatio("0.2999");
    prize2.setName("电视机");
    prizes.add(prize2);

    LdDrawAward prize3 = new LdDrawAward();
    prize3.setId("3");
    prize3.setRatio("99.7");
    prize3.setName("充电宝");
    prizes.add(prize3);

    int times = 1000000;
    int prize1GetTimes = 0;
    int prize2GetTimes = 0;
    int prize3GetTimes = 0;

    for (int i = 0; i < times; i++) {
        LdDrawAward pay = pay(prizes);
        System.out.println("抽奖到了" + pay);
        switch (pay.getId()) {
            case "1":
                prize1GetTimes++;
                break;
            case "2":
                prize2GetTimes++;
                break;
            case "3":
                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);
}

}