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);
}