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);} 
