Java抽奖算法第二例

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;
  }
}

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;
  }

}

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);
  }
}