PHP lottery probability algorithm
php lottery probability algorithm
/* * 不同概率的抽奖原理就是把0到*(比重总数)的区间分块 * 分块的依据是物品占整个的比重,再根据随机数种子来产生0-* 中的某个数 * 判断这个数是落在哪个区间上,区间对应的就是抽到的那个物品。 * 随机数理论上是概率均等的,那么相应的区间所含数的多少就体现了抽奖物品概率的不同。 */ function get_rand($proArr) { $result = array(); foreach ($proArr as $key => $val) { $arr[$key] = $val['v']; } $proSum = array_sum($arr); // 计算总权重 $randNum = mt_rand(1, $proSum); $d1 = 0; $d2 = 0; for ($i=0; $i < count($arr); $i++) { $d2 += $arr[$i]; if($i==0) { $d1 = 0; } else { $d1 += $arr[$i-1]; } if($randNum >= $d1 && $randNum <= $d2) { $result = $proArr[$i]; } } unset ($arr); return $result; } /* * 使用较多的为这个方法 */ function get_rand1($proArr) { $result = array(); foreach ($proArr as $key => $val) { $arr[$key] = $val['v']; } // 概率数组的总概率 $proSum = array_sum($arr); asort($arr); // 概率数组循环 foreach ($arr as $k => $v) { $randNum = mt_rand(1, $proSum); if ($randNum <= $v) { $result = $proArr[$k]; break; } else { $proSum -= $v; } } return $result; }
/* * 奖项数组 * 奖品id,名称,比重 */ $arr = array( array('id'=>1,'name'=>'特等奖','v'=>1), array('id'=>2,'name'=>'一等奖','v'=>5), array('id'=>3,'name'=>'二等奖','v'=>10), array('id'=>4,'name'=>'三等奖','v'=>12), array('id'=>5,'name'=>'四等奖','v'=>22), array('id'=>6,'name'=>'没中奖','v'=>50) ); 测试结果(10000次): get_rand(): count_1:0 count_2:490 count_3:1021 count_4:1172 count_5:2172 count_6:5145 特等奖中奖率全为:0 get_rand1(): count_1:92 count_2:477 count_3:1017 count_4:1195 count_5:2264 count_6:4955 总体感觉 get_rand1() 更准确些......

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