php计算抽奖的概率

<?php 

    //计算抽奖的概率
    function get_rand($proArr) {
        $result = '';
        $proSum = array_sum($proArr);
        foreach ($proArr as $key => $proCur) {
            $randNum = mt_rand(1, $proSum);
            if ($randNum <= $proCur) {
                $result = $key;
                break;
            } else {
                $proSum -= $proCur;
            }
        }
        unset ($proArr);
        return $result;
    }
    $prize_arr = array(
        '0' => array('id'=>1,'prize'=>'1000000514','v'=>2),
        '1' => array('id'=>2,'prize'=>'1000000513','v'=>5),
        '2' => array('id'=>3,'prize'=>'1000000512','v'=>13),
        '3' => array('id'=>4,'prize'=>'1000000511','v'=>15),
        '4' => array('id'=>5,'prize'=>'1000000510','v'=>25),
        '5' => array('id'=>6,'prize'=>'1000000509','v'=>30),
		'6' => array('id'=>7,'prize'=>'1000000508','v'=>10),
    );
    foreach ($prize_arr as $key => $val) {
        $arr[$val['id']] = $val['v'];
    }
    $rid = get_rand($arr);
    $res['yes'] = $prize_arr[$rid-1]['prize'];
    unset($prize_arr[$rid-1]);
    shuffle($prize_arr);
	$prize_arrcount = count($prize_arr);
    for($i=0;$i<$prize_arrcount;$i++){
        $pr[] = $prize_arr[$i]['prize'];
    }
    $res['no'] = $pr;
	//抽奖结果
    $ro = $res['yes'];
	print_r($ro);

?>

php计算抽奖的概率