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PHP lottery probability algorithm

Nov 22, 2016 am 10:37 AM
php

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[&#39;v&#39;]; 
    } 
    // 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;   
}
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/*
 * 奖项数组 
 * 奖品id,名称,比重 
 */

$arr = array(   
    array(&#39;id&#39;=>1,&#39;name&#39;=>&#39;特等奖&#39;,&#39;v&#39;=>1),
    array(&#39;id&#39;=>2,&#39;name&#39;=>&#39;一等奖&#39;,&#39;v&#39;=>5),
    array(&#39;id&#39;=>3,&#39;name&#39;=>&#39;二等奖&#39;,&#39;v&#39;=>10),
    array(&#39;id&#39;=>4,&#39;name&#39;=>&#39;三等奖&#39;,&#39;v&#39;=>12),
    array(&#39;id&#39;=>5,&#39;name&#39;=>&#39;四等奖&#39;,&#39;v&#39;=>22),
    array(&#39;id&#39;=>6,&#39;name&#39;=>&#39;没中奖&#39;,&#39;v&#39;=>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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