php敏感キーワードフィルタリング

$badword = array(
    '  ','   ','    ','  '
);
$badword1 = array_combine($badword,array_fill(0,count($badword),'*'));
$bb = '           ';
$str = strtr($bb, $badword1);
echo $str;

 
 
 
 

$hei=array(
    '  ',
    '  '
);
$blacklist="/".implode("|",$hei)."/i";
$str="           ";
if(preg_match($blacklist, $str, $matches)){
    print "found:". $matches[0];
} else {
    print "not found.";
}