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

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);
}

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