php实现概率性随机抽奖代码

1、初始数据：

权重越大，抽取的几率越高
[奖品1， 权重 5], [ 奖品2， 权重6]， [ 奖品3， 权重 7]， [ 奖品4， 权重2]

2、处理步骤：

1）n = 5 + 6 + 7 + 2 = 20
2）然后取1-n的随机数m
3）界定各 奖品的权重范围值 奖品 1 ： 1-5 ; 奖品2 ： 6-11； 奖品3： 12-18； 奖品4： 19-20
4) 如果m在某个奖品的权重范围值内，标识这个奖品被抽取到

<?php
/**
 * 奖品
 */
class prize {
  # id
  public $id = null;
  # 权重
  public $weight = null;
  # 奖品名
  public $name = null;
 
  # 权重范围区间起始值
  protected $start = 0;
  # 权重范围区间结束值
  protected $end = 0;
 
  public function __construct($id, $weight, $name) {
    if (!$id) {
      throw new exception('奖品id为空.');
    }
    $this->id = $id;
    $this->weight = $weight ? $weight : 0;
    $this->name = $name ? $name : '随机奖品' . $id;
  }
 
  # id
  public function getid() {
    return $this->id;
  }
 
  # 权重
  public function getweight() {
    return $this->weight;
  }
 
  # 设置权重范围区间
  public function setrange($start, $end) {
    $this->start = $start;
    $this->end = $end;
  }
 
  # 判断随机数是否在权重范围区间
  public function inrange($num) {
    return ($num >= $this->start) && ($num <= $this->end);
  }
}
 
/**
 * 奖品池
 */
class prizepoll implements iteratoraggregate, countable {
  # 奖品集
  protected $items = array();
 
  # 加入奖品
  public function additem(prize $item) {
    $this->items[$item->getid()] = $item;
    return $this;
  }
 
  # 删除奖品
  public function removeitem($itemid) {
    if (isset($this->items[$itemid])) {
      unset($this->items[$itemid]);
    }
    return $this;
  }
 
  # 更新奖品
  public function updateitem(prize $item) {
    if (isset($this->items[$item->getid()])) {
      $this->items[$item->getid()] = $item;
    }
    return $this;
  }
 
  # 获取所有奖品
  public function getitems() {
    return $this->items;
  }
 
  # 所有所有可用奖品(如果权重为0，说明这个奖品永远不可能抽到)
  public function getvisibleitems() {
    $items = array();
    foreach ($this->items as $item) {
      if ($item->getweight()) {
        $items[$item->getid()] = $item;
      }
    }
    return $items;
  }
 
  # countable::count
  public function count() {
    return count($this->items);
  }
 
  # iteratoraggregate::getiterator()
  public function getiterator() {
    return new arrayiterator($this->items);
  }
}
 
/**
 * 简单的抽奖类
 */
class simpleturn {
  # 奖池
  protected $poll = null;
   
  public function __construct(prizepoll $poll) {
    if ($poll) {
      $this->setpoll($poll);
    }
  }
 
  # 抽奖
  public function run(prizepoll $poll) {
    $poll = $poll ? $poll : $this->poll;
    if ( ! $poll) {
      throw new exception('奖池未初始化');
    }
 
    if ($poll->count() <= 0) {
      throw new exception('奖池为空');
    }
 
    $items = $poll->getvisibleitems();
    if (count($items) <= 0) {
      throw new exception('奖池为空');
    }
 
    $sum = 0;
    foreach ($items as $item) {
      $start = $sum + 1;
      $sum += $item->getweight();
      $end = $sum;
 
      # 设置奖品的权重范围区间
      $item->setrange($start, $end);
    }
 
    # 随机数
    $rand = $this->getrandnum(1, $sum);
 
    # 区间段判断
    foreach ($items as $item) {
      if ($item->inrange($rand)) {
        return $item;
      }
    }
    return null;
  }
 
  # 获取随机数
  public function getrandnum($min, $max) {
    return mt_rand($min ? $min : 1, $max);
  }
 
  # 设置奖池
  public function setpoll(prizepoll $poll) {
    $this->poll = $poll;
  }
}
 
# 示例
try {
  $prizepoll = new prizepoll();
  $prizepoll->additem(new prize(1, 5))
    ->additem(new prize(2, 6))
    ->additem(new prize(3, 7))
    ->additem(new prize(4, 2));
 
  $turn = new simpleturn($prizepoll);
  $prize = $turn->run();
  var_dump($prize);
} catch (exception $e) {
  print_r($e);
}