1、初始資料：
權重越大，抽取的幾率越高
[獎品1， 權重 5], [ 獎品2， 權重6]， [ 獎品3， 權重 7]， [ 獎品4， 權重2]
2、處理步驟：
1)N = 5 + 6 + 7 + 2 = 20
2)然後取1-N的随機數M
3)界定各 獎品的權重範圍值 獎品 1 ： 1-5 ; 獎品2 ： 6-11； 獎品3： 12-18； 獎品4： 19-20
4) 如果M在某個獎品的權重範圍值内，辨別這個獎品被抽取到
class Prize {
# ID
public $id = null;
# 權重
public $weight = null;
# 獎品名
public $name = null;
# 權重範圍區間起始值
protected $start = 0;
# 權重範圍區間結束值
protected $end = 0;
public function __construct($id, $weight, $name) {
if (!$id) {
throw new Exception('獎品ID為空.');
}
$this->id = $id;
$this->weight = $weight ? $weight : 0;
$this->name = $name ? $name : '随機獎品' . $id;
}
# id
public function getId() {
return $this->id;
}
# 權重
public function getWeight() {
return $this->weight;
}
# 設定權重範圍區間
public function setRange($start, $end) {
$this->start = $start;
$this->end = $end;
}
# 判斷随機數是否在權重範圍區間
public function inRange($num) {
return ($num >= $this->start) && ($num <= $this->end);
}
}
class PrizePoll implements IteratorAggregate, Countable {
# 獎品集
protected $items = array();
# 加入獎品
public function addItem(Prize $item) {
$this->items[$item->getId()] = $item;
return $this;
}
# 删除獎品
public function removeItem($itemId) {
if (isset($this->items[$itemId])) {
unset($this->items[$itemId]);
}
return $this;
}
# 更新獎品
public function updateItem(Prize $item) {
if (isset($this->items[$item->getId()])) {
$this->items[$item->getId()] = $item;
}
return $this;
}
# 擷取所有獎品
public function getItems() {
return $this->items;
}
# 所有所有可用獎品(如果權重為0，說明這個獎品永遠不可能抽到)
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);
}
}
class SimpleTurn {
# 獎池
protected $poll = null;
public function __construct(PrizePoll $poll) {
if ($poll) {
$this->setPoll($poll);
}
}
# 抽獎
public function run(PrizePoll $poll) {
$poll = $poll ? $poll : $this->poll;
if ( ! $poll) {
throw new Exception('獎池未初始化');
}
if ($poll->count() <= 0) {
throw new Exception('獎池為空');
}
$items = $poll->getVisibleItems();
if (count($items) <= 0) {
throw new Exception('獎池為空');
}
$sum = 0;
foreach ($items as $item) {
$start = $sum + 1;
$sum += $item->getWeight();
$end = $sum;
# 設定獎品的權重範圍區間
$item->setRange($start, $end);
}
# 随機數
$rand = $this->getRandNum(1, $sum);
# 區間段判斷
foreach ($items as $item) {
if ($item->inRange($rand)) {
return $item;
}
}
return null;
}
# 擷取随機數
public function getRandNum($min, $max) {
return mt_rand($min ? $min : 1, $max);
}
# 設定獎池
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);
}