我们先完成后台PHP的流程，PHP的主要工作是负责配置奖项及对应的中奖概率，当前端页面点击翻动某个方块时会想后台PHP发送ajax请求，那么后台PHP根据配置的概率，通过概率算法给出中奖结果，同时将未中奖的奖项信息一并以JSON数据格式发送给前端页面。
先来看概率计算函数
<span> 1</span> <span>function</span> get_rand(<span>$proArr</span><span>) {
</span><span> 2</span> <span>$result</span> = ''<span>;
</span><span> 3</span>
<span> 4</span> <span>//</span><span>概率数组的总概率精度 </span>
<span> 5</span> <span>$proSum</span> = <span>array_sum</span>(<span>$proArr</span><span>);
</span><span> 6</span>
<span> 7</span> <span>//</span><span>概率数组循环 </span>
<span> 8</span> <span>foreach</span> (<span>$proArr</span> <span>as</span> <span>$key</span> => <span>$proCur</span><span>) {
</span><span> 9</span> <span>$randNum</span> = <span>mt_rand</span>(1, <span>$proSum</span><span>);
</span><span>10</span> <span>if</span> (<span>$randNum</span> <= <span>$proCur</span><span>) {
</span><span>11</span> <span>$result</span> = <span>$key</span><span>;
</span><span>12</span> <span>break</span><span>;
</span><span>13</span> } <span>else</span><span> {
</span><span>14</span> <span>$proSum</span> -= <span>$proCur</span><span>;
</span><span>15</span> <span> }
</span><span>16</span> <span> }
</span><span>17</span> <span>unset</span> (<span>$proArr</span><span>);
</span><span>18</span>
<span>19</span> <span>return</span> <span>$result</span><span>;
</span><span>20</span> }
上述代码是一段经典的概率算法，$proArr是一个预先设置的数组，假设数组为：array(100,200,300，400)，开始是从1,1000这个概率范围内筛选第一个数是否在他的出现概率范围之内， 如果不在，则将概率空间，也就是k的值减去刚刚的那个数字的概率空间，在本例当中就是减去100，也就是说第二个数是在1，900这个范围内筛选的。这样筛选到最终，总会有一个数满足要求。就相当于去一个箱子里摸东西，第一个不是，第二个不是，第三个还不是，那最后一个一定是。这个算法简单，而且效率非常高，关键是这个算法已在我们以前的项目中有应用，尤其是大数据量的项目中效率非常棒。
接下来我们通过PHP配置奖项。
<span>1</span> <span>$prize_arr</span> = <span>array</span><span>(
</span><span>2</span> '0' => <span>array</span>('id'=>1,'prize'=>'平板电脑','v'=>1),
<span>3</span> '1' => <span>array</span>('id'=>2,'prize'=>'数码相机','v'=>5),
<span>4</span> '2' => <span>array</span>('id'=>3,'prize'=>'音箱设备','v'=>10),
<span>5</span> '3' => <span>array</span>('id'=>4,'prize'=>'4G优盘','v'=>12),
<span>6</span> '4' => <span>array</span>('id'=>5,'prize'=>'10Q币','v'=>22),
<span>7</span> '5' => <span>array</span>('id'=>6,'prize'=>'下次没准就能中哦','v'=>50),
<span>8</span> ); 该二维数组，记录了所有本次抽奖的奖项信息，其中id表示中奖等级，prize表示奖品，v表示中奖概率。注意其中的v必须为整数，你可以将对应的奖项的v设置成0，即意味着该奖项抽中的几率是0，数组中v的总和（基数），基数越大越能体现概率的准确性。本例中v的总和为100，那么平板电脑对应的中奖概率就是1%，如果v的总和是10000，那中奖概率就是万分之一了。
每次前端页面的请求，PHP循环奖项设置数组，通过概率计算函数get_rand获取抽中的奖项id。将中奖奖品保存在数组$res['yes']中，而剩下的未中奖的信息保存在$res['no']中，最后输出json个数数据给前端页面。
<span> 1</span> <span>foreach</span> (<span>$prize_arr</span> <span>as</span> <span>$key</span> => <span>$val</span><span>) {
</span><span> 2</span> <span>$arr</span>[<span>$val</span>['id']] = <span>$val</span>['v'<span>];
</span><span> 3</span> <span>}
</span><span> 4</span>
<span> 5</span> <span>$rid</span> = get_rand(<span>$arr</span>); <span>//</span><span>根据概率获取奖项id </span>
<span> 6</span>
<span> 7</span> <span>$res</span>['yes'] = <span>$prize_arr</span>[<span>$rid</span>-1]['prize']; <span>//</span><span>中奖项 </span>
<span> 8</span> <span>unset</span>(<span>$prize_arr</span>[<span>$rid</span>-1]); <span>//</span><span>将中奖项从数组中剔除，剩下未中奖项 </span>
<span> 9</span> <span>shuffle</span>(<span>$prize_arr</span>); <span>//</span><span>打乱数组顺序 </span>
<span>10</span> <span>for</span>(<span>$i</span>=0;<span>$i</span><<span>count</span>(<span>$prize_arr</span>);<span>$i</span>++<span>){
</span><span>11</span> <span>$pr</span>[] = <span>$prize_arr</span>[<span>$i</span>]['prize'<span>];
</span><span>12</span> <span>}
</span><span>13</span> <span>$res</span>['no'] = <span>$pr</span><span>;
</span><span>14</span> <span>echo</span> json_encode(<span>$res</span>);
