package com.zyan.local.pojo.entity;
import lombok.Data;
import java.io.Serializable;
import java.math.BigDecimal;
/**
 * @author zyan
 * @since 2022/12/16 16:49 星期五
 */
@Data
public class Prize implements Serializable {
    public Prize(Integer id, String name, Integer weight) {
        this.id = id;
        this.name = name;
        this.weight = weight;
    }
    /**
     * id
     */
    private Integer id;
    /**
     * 名稱
     */
    private String name;
    /**
     * 權(quán)重
     */
    private Integer weight;
}

public static Prize lottery(List<Prize> prizeList) {
    //按照權(quán)重從小到大排序獎(jiǎng)品
    prizeList.sort(Comparator.comparingInt(Prize::getWeight));
    //計(jì)算節(jié)點(diǎn) 節(jié)點(diǎn)的數(shù)量比獎(jiǎng)品的數(shù)量多一個(gè)，即0
    List<Integer> nodeList = new ArrayList<>();
    //第一個(gè)節(jié)點(diǎn)為0
    nodeList.add(0);
    for (Prize prize : prizeList) {
        //每一個(gè)節(jié)點(diǎn)等于前一個(gè)節(jié)點(diǎn)+當(dāng)前獎(jiǎng)品的權(quán)重
        nodeList.add(nodeList.get(nodeList.size() - 1) + prize.getWeight());
    }
    //生成 0-結(jié)束節(jié)點(diǎn) 的隨機(jī)數(shù)
    int randomInt = RandomUtil.randomInt(0, nodeList.get(nodeList.size() - 1));
    //最終抽獎(jiǎng)邏輯 此處需要從第二個(gè)節(jié)點(diǎn)開始遍歷
    for (int i = 1; i < nodeList.size(); i++) {
        //本次節(jié)點(diǎn)
        Integer endNode = nodeList.get(i);
        //前一個(gè)節(jié)點(diǎn)
        Integer startNode = nodeList.get(i - 1);
        //若隨機(jī)數(shù)大于等于前一個(gè)節(jié)點(diǎn)并且小于本節(jié)點(diǎn)，在prizeList中位于i-1位置的獎(jiǎng)品為抽中獎(jiǎng)品
        //Tip：比較大小時(shí)，左閉右開與左開右閉都可以，不影響整體概率
        if (randomInt >= startNode
                && randomInt < endNode) {
            return prizeList.get(i - 1);
        }
    }
    throw new RuntimeException("程序異常 生成的隨機(jī)數(shù)不在任何獎(jiǎng)品區(qū)間內(nèi)");
}

public static void main(String[] args) {
    List<Prize> prizeList = new ArrayList<>();
    prizeList.add(new Prize(0, "獎(jiǎng)品0", 2300));
    prizeList.add(new Prize(1, "獎(jiǎng)品1", 200));
    prizeList.add(new Prize(2, "獎(jiǎng)品2", 500));
    prizeList.add(new Prize(3, "獎(jiǎng)品3", 800));
    prizeList.add(new Prize(4, "獎(jiǎng)品4", 800));
    //進(jìn)行一千次抽獎(jiǎng)驗(yàn)證概率
    List<Prize> lotteryResult = new ArrayList<>();
    for (int i = 0; i <= 1000; i++) {
        lotteryResult.add(lottery(prizeList));
    }
    Map<String, List<Prize>> collect = lotteryResult.stream().collect(Collectors.groupingBy(Prize::getName));
    collect.forEach((k, v) -> System.out.println(k + " 被抽中 " + v.size() + " 次"));
}