function getCombinations($array) {

        //initalize array
        $results = [[]];

        //get all combinations
        foreach ($array as $k => $element) {
            foreach ($results as $combination){
                $results[] =  $combination + [$k => $element];}
        }

        //return filtered array
        return array_values(array_filter($results));

    }

function prima($str,$haystack){
  if ($str != '')
    {
      if (count($haystack)>0)
      {
         $a = array();
         for($i=0; $i<count($haystack);$i++)
         {
             if (stripos($str, $haystack[$i]) !== false)
             {
               array_push($a,$haystack[$i]);

             }
             //var_dump($haystack[$i]);
         }
          if (count($a) > 3)
          {
              $arr = getCombinations($a);
              for($j=0; $j<count($arr); $j++)
              {
              if (implode('',$arr[$j]) === $str)
              {
                print implode(';',$arr[$j]). "<br />";
              }
              }

           }
         else print implode(';',$a). "<br />";
      }
  }

}

$regex = array('pro', 'gram', 'program', 'programmer', 'merit','it');