概率计算

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  • 算法一
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/**
 * 全概率计算
 *
 * @param array $p array('a'=>0.5,'b'=>0.2,'c'=>0.4)
 * @return string 返回上面数组的key
 */
function random($ps){
    static $arr = array();
    $key = md5(serialize($ps));

    if (!isset($arr[$key])) {
        $max = array_sum($ps);
        foreach ($ps as $k=>$v) {
            $v = $v / $max * 10000;
            for ($i=0; $i<$v; $i++) $arr[$key][] = $k;
        }
    }
    return $arr[$key][mt_rand(0,count($arr[$key])-1)];
}
  • 算法二
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/**
 * 根据权重概率获取
 * @param $weights [ { k => weight } ]
 * @return int|string
 */
public function getRand( $weights )
{
	$result = '';

	$weightSum = array_sum( $weights );

	foreach( $weights as $key => $weight )
	{
		$randNum = mt_rand( 1, $weightSum );
		if( $randNum <= $weight )
		{
			$result = $key;
			break;
		}
		$weightSum -= $weight;
	}

	return $result;
}