Java 抽奖算法

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

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1. public class Arithmetic {    // 放大倍数    private static final int mulriple = 1000000;    public int pay(List<Prize> prizes) {        int lastScope = 0;        // 洗牌，打乱奖品次序        Collections.shuffle(prizes);        Map<Integer, int[]> prizeScopes = new HashMap<Integer, int[]>();        Map<Integer, Integer> prizeQuantity = new HashMap<Integer, Integer>();        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<Entry<Integer, int[]>> entrySets = prizeScopes.entrySet();            for (Map.Entry<Integer, int[]> m : entrySets) {                int key = m.getKey();                if (luckyNumber >= m.getValue()[0] && luckyNumber <= m.getValue()[1] && prizeQuantity.get(key) > 0) {                    luckyPrizeId = key;                    break;                }            }        }        if (luckyPrizeId > 0) {            // 奖品库存减一        }        return luckyPrizeId;    }}  

Prize bean

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1. 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;    public Integer getPrizeId() {        return prizeId;    }    public void setPrizeId(Integer prizeId) {        this.prizeId = prizeId;    }    public BigDecimal getProbability() {        return probability;    }    public void setProbability(BigDecimal probability) {        this.probability = probability;    }    public Integer getQuantity() {        return quantity;    }    public void setQuantity(Integer quantity) {        this.quantity = quantity;    }}  

3. 测试

prize1概率: 5%

prize2概率: 10%

prize3概率: 15%

prize4概率: 20%

prize5概率: 50%

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1. public class Test {    public static void main(String[] args) {        List<Prize> prizes = new ArrayList<Prize>();        Prize prize1 = new Prize();        prize1.setPrizeId(1);        prize1.setProbability(new BigDecimal(0.05));        prize1.setQuantity(1);        prizes.add(prize1);        Prize prize2 = new Prize();        prize2.setPrizeId(2);        prize2.setProbability(new BigDecimal(0.10));        prize2.setQuantity(10);        prizes.add(prize2);        Prize prize3 = new Prize();        prize3.setPrizeId(3);        prize3.setProbability(new BigDecimal(0.15));        prize3.setQuantity(20);        prizes.add(prize3);        Prize prize4 = new Prize();        prize4.setPrizeId(4);        prize4.setProbability(new BigDecimal(0.20));        prize4.setQuantity(50);        prizes.add(prize4);        Prize prize5 = new Prize();        prize5.setPrizeId(5);        prize5.setProbability(new BigDecimal(0.50));        prize5.setQuantity(200);        prizes.add(prize5);        int prize1GetTimes = 0;        int prize2GetTimes = 0;        int prize3GetTimes = 0;        int prize4GetTimes = 0;        int prize5GetTimes = 0;        Arithmetic arithmetic = new Arithmetic();        int times = 1000;        for (int i = 0; i < times; i++) {            int prizeId = arithmetic.pay(prizes);            switch (prizeId) {                case 1:                    prize1GetTimes++;                    break;                case 2:                    prize2GetTimes++;                    break;                case 3:                    prize3GetTimes++;                    break;                case 4:                    prize4GetTimes++;                    break;                case 5:                    prize5GetTimes++;                    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);        System.out.println("prize4中奖次数" + prize4GetTimes);        System.out.println("prize5中奖次数" + prize5GetTimes);    }}  

结果：

通过1000次抽取，我们看出算法精度还是很高的。