detect a string contained by another discontinuously

Recently I'm working on bad content(such as advertise post) filter of a BBS.And I write a functio开发者_StackOverflown to detect a string is in another string not continuously.Code as below:

$str = 'helloguys';
$substr1 = 'hlu';
$substr2 = 'elf';

function detect($a,$b) //function that detect a in b
{
    $c = '';
    for($i=0;$i<=strlen($a);$i++)
    {
        for($j=0;$j<=strlen($b);$j++)
        {
            if($a[$i] == $b[$j])
            {
               $b=substr($b,$j+1);
               $c .=$a[$i];
               break;
            }
        }
    }
    if($c == $a) return true;
    else return false;
}

var_dump(detect($substr1,$str)); //true
var_dump(detect($substr2,$str)); //false

Since the filter works before the users do their posts so I think the efficiency here is important.And I wonder if there's any better solution? Thanks!

---

a faster way to do this is converting $a to a regular expression and match it with $b, so that you just leave the optimization to the PCRE module itself which is written in C code.

for example:

detect("hlu",$b) is equal to preg_match("/h.*l.*u/", $b)
(detect("hlu",$b) && detect("elf",$b)) is equal to preg_match("/(h.*l.*u|e.*l.*f)/", $b)

---

not sure why you would want to do this. but i was bored

function detect( $a,$b ) {

    return count( array_intersect( str_split($b), str_split($a) ) ) == strlen($b);

}