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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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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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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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。