PHP抽獎程序概率算法

//概率算法,6個獎項
$prize_arr = array(
    '0' => array('id'=>1,'prize'=>'iphone6','v'=>1),
    '1' => array('id'=>2,'prize'=>'數碼相機','v'=>5),
    '2' => array('id'=>3,'prize'=>'音箱設備','v'=>10),
    '3' => array('id'=>4,'prize'=>'50Q幣','v'=>24),
    '4' => array('id'=>5,'prize'=>'10Q幣','v'=>60),
    '5' => array('id'=>6,'prize'=>'干吧碟','v'=>1900),
);

//每個獎品的中獎幾率,獎品ID作為數組下標
foreach($prize_arr as $val){
    $item[$val['id']] = $val['v'];
}
function get($item){
    //中獎概率基數 
    $num = array_sum($item);//當前一等獎概率1/2000

foreach($item as $k=>$v){
    //獲取一個1到當前基數范圍的隨機數
    $rand = mt_rand(1,$num);
    if($rand <= $v){
        //假設當前獎項$k=2,$v<=5才能中獎
        $res = $k;
        break;
    }else{
        //假設當前獎項$k=6,$v>1900,則沒中六等獎,總獲獎基數2000-1900,前五次循環都沒中則2000-1-5-10-24-60=1900,必中6等獎,哈哈
        $num -= $v;
    }
}
return $res;

}
$res = get($item);
$h = $prize_arr[$res-1]['prize'];
echo $h.'; ';</pre>