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HomeBackend DevelopmentPHP TutorialSummary of PHP probability calculation functions_php skills

其实发这篇博感觉并没有什么用,太简单了,会的人不屑看,不会的人自已动动脑子也想到了。但是看着自已的博客已经这么久没更,真心疼~。粗略算下一篇只有代码的水文,会占用OSC至少十几KB的数据库空间呢,但是,一想到乱弹里的然并卵,也就释然了。

<&#63;php
 
/**
 * 概率计算类
 * 可用于抽奖等
 */
class Probability
{
  /**
   * 概率统计数据
   * thing => chance
   */
  var $data = array();
  var $chance_count = 0;
 
  function __construct($initdata = array()){
    if(!empty($initdata)){
      $this->data = $initdata;
      foreach($initdata as $d){
        $this->chance_count += $d['num'];
      }
    }
  }
 
  function addData($name, $chance){
    $this->data[]=array('name'=>$name, 'num'=>$chance);
    $this->chance_count += $chance;
  }
 
  function getOne(){
    $index = rand(0, $this->chance_count);
    foreach($this->data as $d){
      $index = $index-$d['num'];
      if($index<=0){
        return $d['name'];
      }
    }
    return '';
  }
}
 
 
/**
 * 使用示例
 */
$pro=new Probability();
$pro->addData('iphone',10);
$pro->addData('watch',30);
$pro->addData('$18',50);
$pro->addData('thank you',10);
$pro->addData('super big',1);
for($i=0;$i<100;$i++){
  echo $pro->getOne()."\n";
}

这是一个很经典的概率算法函数:

function get_rand($proArr) { 
  $result = ''; 
  //概率数组的总概率精度 
  $proSum = array_sum($proArr); 
  //概率数组循环 
  foreach ($proArr as $key => $proCur) { 
    $randNum = mt_rand(1, $proSum);       //抽取随机数
    if ($randNum <= $proCur) { 
      $result = $key;             //得出结果
      break; 
    } else { 
      $proSum -= $proCur;           
    } 
  } 
  unset ($proArr); 
  return $result; 
}

假设:我们有这样一个数组:a奖概率20%,b奖概率30%,c奖概率50%

$prize_arr =array('a'=>20,'b'=>30,'c'=>50);

模拟函数执行过程:

总概率精度为20+30+50=100

第一次数组循环,$procur=20

假设抽取的随机数rand(1,100),假设抽到$randNum=55

if判断-------

如果$randNum

否则进入下一循环,总概率精度变为100-20=80

第二次数组循环,$procur=30

假设抽取的随机数rand(1,80),假设抽到$randNum=33

if判断---------

如果$randNum

否则进入下一循环,总概率精度变为80-30=50

第三次数组循环,$prosur=50;

假设抽取的随机数rand(1,50),不管怎么抽,随机数都会

那么得出result=c;

 因为样本没有改变,虽然可能抽取的随机数不止一个,但是概率是不变的。

或者也可以这样:

  function get_rand($arr)
  {
    $pro_sum=array_sum($arr);
    $rand_num=mt_rand(1,$pro_sum);
    $tmp_num=0;
    foreach($arr as $k=>$val)
    {  
      if($rand_num<=$val+$tmp_num)
      {
        $n=$k;
        break;
      }else
      {
        $tmp_num+=$val;
      }
    }
    return $n;
  }

在给大家分享一个抽奖的概率算法

/*
 * 经典的概率算法,
 * $proArr是一个预先设置的数组,
 * 假设数组为:array(100,200,300,400),
 * 开始是从1,1000 这个概率范围内筛选第一个数是否在他的出现概率范围之内, 
 * 如果不在,则将概率空间,也就是k的值减去刚刚的那个数字的概率空间,
 * 在本例当中就是减去100,也就是说第二个数是在1,900这个范围内筛选的。
 * 这样 筛选到最终,总会有一个数满足要求。
 * 就相当于去一个箱子里摸东西,
 * 第一个不是,第二个不是,第三个还不是,那最后一个一定是。
 * 这个算法简单,而且效率非常 高,
 * 关键是这个算法已在我们以前的项目中有应用,尤其是大数据量的项目中效率非常棒。
 */
function get_rand($proArr) {
  $result = '';
  //概率数组的总概率精度 
  $proSum = array_sum($proArr);
  //概率数组循环 
  foreach ($proArr as $key => $proCur) {
    $randNum = mt_rand(1, $proSum);
    if ($randNum <= $proCur) {
      $result = $key;
      break;
    } else {
      $proSum -= $proCur;
    }
  }
  unset ($proArr);
  return $result;
}
 
 
/*
 * 奖项数组
 * 是一个二维数组,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。
 * 
 */
$prize_arr = array(
  '0' => array('id'=>1,'prize'=>'平板电脑','v'=>1),
  '1' => array('id'=>2,'prize'=>'数码相机','v'=>5),
  '2' => array('id'=>3,'prize'=>'音箱设备','v'=>10),
  '3' => array('id'=>4,'prize'=>'4G优盘','v'=>12),
  '4' => array('id'=>5,'prize'=>'10Q币','v'=>22),
  '5' => array('id'=>6,'prize'=>'下次没准就能中哦','v'=>50),
);
 
/*
 * 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。
 */
foreach ($prize_arr as $key => $val) {
  $arr[$val['id']] = $val['v'];
}
$rid = get_rand($arr); //根据概率获取奖项id 
 
$res['yes'] = $prize_arr[$rid-1]['prize']; //中奖项 
unset($prize_arr[$rid-1]); //将中奖项从数组中剔除,剩下未中奖项 
shuffle($prize_arr); //打乱数组顺序 
for($i=0;$i<count($prize_arr);$i++){
  $pr[] = $prize_arr[$i]['prize'];
}
$res['no'] = $pr;
print_r($res['yes']);

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