1、初始數據：
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）然后取1-N的隨機數M
3）界定各 獎品的權重范圍值 獎品 1 ： 1-5 ; 獎品2 ： 6-11； 獎品3： 12-18； 獎品4： 19-20
4) 如果M在某個獎品的權重范圍值內，標識這個獎品被抽取到
<?php/** * 獎品 */class Prize { # ID public $id = null; # 權重 public $weight = null; # 獎品名 public $name = null; # 權重范圍區間起始值 protected $start = 0; # 權重范圍區間結束值 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 : '隨機獎品' . $id; } # id public function getId() { return $this->id; } # 權重 public function getWeight() { return $this->weight; } # 設置權重范圍區間 public function setRange($start, $end) { $this->start = $start; $this->end = $end; } # 判斷隨機數是否在權重范圍區間 public function inRange($num) { return ($num >= $this->start) && ($num <= $this->end); }} /** * 獎品池 */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 $this; } # 刪除獎品 public function removeItem($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; } # 獲取所有獎品 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); }} /** * 簡單的抽獎類 */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; # 設置獎品的權重范圍區間 $item->setRange($start, $end); } # 隨機數 $rand = $this->getRandNum(1, $sum); # 區間段判斷 foreach ($items as $item) { if ($item->inRange($rand)) { return $item; } } return null; } # 獲取隨機數 public function getRandNum($min, $max) { return mt_rand($min ? $min : 1, $max); } # 設置獎池 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);} 
