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);
    }
}