php中如何計算抽獎的機率

<?php             //計算抽獎的機率      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;         //抽獎結果      $ro = $res['yes'];      print_r($ro);                            ?>

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