实现概率抽奖

package com.weiease.app.service.luckydraw;

import lombok.Data;
import lombok.experimental.Accessors;

import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;

/**
 * @author huhuszl
 * @version 1.0
 * @date 2023/9/27 11:16
 * @description 概率抽奖工具类
 */
public class ProbabilityDrawUtils {
    @Data
    @Accessors(chain = true)
    public static class ProbabilityEntity<T> {
        private T entity; // 实体
        private Integer id; // id 区别实体的id，每个实体保证唯一
        private Double ProbabilityValue; // 概率值
    }

    /**
     * 概率性抽奖
     *
     * @param probabilityEntityList 概率配置列表
     * @param defaultValue          不符条件返回的默认结果
     * @param <T>                   抽奖的实体
     * @return 返回中奖实体
     */
    public static <T> ProbabilityEntity<T> probabilityLottery(List<ProbabilityEntity<T>> probabilityEntityList, ProbabilityEntity<T> defaultValue) {
        // 公平性检测
        double sum = probabilityEntityList.stream().mapToDouble(ProbabilityEntity::getProbabilityValue).summaryStatistics().getSum();
        if (sum != 1.00) {
            probabilityEntityList.forEach(r -> {
                r.setProbabilityValue(r.getProbabilityValue() / sum);
            });
        }
        Double minRate = probabilityEntityList.get(0).getProbabilityValue();
        // 找到最小值，保证可中
        for (ProbabilityEntity<T> item : probabilityEntityList) {
            if (minRate > item.getProbabilityValue()) {
                minRate = item.getProbabilityValue();
            }
        }
        // 找到区间最大值
        Integer speed = 1;
        while (!((minRate * speed) > 1)) {
            speed = speed * 10;
        }
        Map<Integer, List<Integer>> map = new HashMap<>();
        int startIndex = 1;
        for (ProbabilityEntity<T> item : probabilityEntityList) {
            List<Integer> data = new ArrayList<>();
            data.add(startIndex);
            int endIndex = startIndex + (int) (speed * item.getProbabilityValue());
            data.add(endIndex);
            map.put(item.getId(), data);
            startIndex = endIndex + 1;
        }
        // 判断值在那个区间
        Random random = new Random();
        int r = random.nextInt(speed);
        for (Map.Entry<Integer, List<Integer>> entry : map.entrySet()) {
            if (entry.getValue().get(0) <= r && r <= entry.getValue().get(1)) {
                List<ProbabilityEntity<T>> entities = probabilityEntityList.stream().filter(e -> e.getId().equals(entry.getKey())).collect(Collectors.toList());
                if (entities.size() > 0) {
                    return entities.get(0);
                }
            }
        }
        return defaultValue;
    }

    public static void main(String[] args) {
        List<ProbabilityEntity<String>> probabilityEntities = new ArrayList<>();
        probabilityEntities.add(new ProbabilityEntity<String>().setProbabilityValue(0.00001).setId(1).setEntity("电脑"));
        probabilityEntities.add(new ProbabilityEntity<String>().setProbabilityValue(0.001).setId(2).setEntity("手机"));
        probabilityEntities.add(new ProbabilityEntity<String>().setProbabilityValue(0.02).setId(3).setEntity("ipad"));
        probabilityEntities.add(new ProbabilityEntity<String>().setProbabilityValue(0.1).setId(4).setEntity("谢谢惠顾"));
        probabilityEntities.add(new ProbabilityEntity<String>().setProbabilityValue(0.1).setId(5).setEntity("1元优惠券"));
        ProbabilityEntity<String> defaultThanks = new ProbabilityEntity<String>().setEntity("谢谢惠顾")
                .setId(4).setProbabilityValue(0.0);
        Map<String, Integer> prizeMap = new HashMap<>();
        for (int i = 0; i < 1000000; i++) {
            ProbabilityEntity<String> entity = probabilityLottery(probabilityEntities, defaultThanks);
            AtomicInteger atomicI;
            if (prizeMap.get(entity.getEntity()) == null) {
                atomicI = new AtomicInteger(0);
            } else {
                atomicI = new AtomicInteger(prizeMap.get(entity.getEntity()));
            }
            if (entity.getId() == 1) {
                System.out.println(i);
            }
            prizeMap.put(entity.getEntity(), atomicI.incrementAndGet());
        }
        System.out.println(prizeMap);
    }
}