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);}