PHP code to get the substring with the most occurrences in a Chinese string

/***
**The length of the substring can be customized, such as 4 consecutive characters
**site http://bbs.it-home.org
 $str =' I am Chinese I am foreigner I am Korean I am American I am Chinese I am British I am Chinese I am foreigner';
 Count_string($str,5);
 function Count_string($sstr, $length)
 {
 $cnt_tmp = 0;
 $cnt = 0;
 $str = '';
 $str_tmp = array();
 $str_arr = array();
 mb_internal_encoding("gb2312");
 $ max_length = (mb_strlen($sstr)-$length);

 //Get the substring set
 for($i=0;$i<=$max_length;$i++)
 {
 $str_tmp[] = mb_substr($ sstr, $i, $length);
 }
 //Remove duplicate substrings
 $str_tmp = array_unique($str_tmp);

 //Calculate the number of occurrences
 foreach($str_tmp as $key=>$value)
 {
 $cnt_tmp = mb_substr_count($sstr,$value);
 if($cnt_tmp>=$cnt)
 {
 $cnt = $cnt_tmp;
 $str_arr[$value] = $cnt;
 }
 }

 //Handle multiple results
 foreach($str_arr as $key=>$value)
 {
 if($value == $cnt)
 {$str .=$key."";}
 }

 echo 'The most frequently occurring substring is:'.$str.'Number of occurrences:'.$cnt;
}
?>

Yes Interested friends can also refer to this article: php calculates the code for the most frequent characters in a string of unknown length.