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Java抽奖算法第二例

2019年07月22日  | 移动技术网IT编程  | 我要评论

本文实例为大家分享了java抽奖算法，供大家参考，具体内容如下

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 

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

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% 


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。

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