依据奖品权重值实现的随机抽奖，PHP实现

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
3、具体代码实现

<?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()])) {
$this->items[$itemId->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);
}