Question

I have some input string with characters and list of string. What I need is to select only strings that meet pattern that contains characters.
For excample:

input chars = “ask”
it should accept “ask”, “sak”, “kas”…
but should not accept “akk”, “aas”…

now I use pattern like “^[s|a|k][s|a|k][s|a|k]$”
but probablem with it that it accept and repeated characters (“akk”), so if I using this I need some additional check if preg_match works.

What it makes a bit more complicated, that there can be few same characters:
input “askk”
should match “akks”, but not “kkks” or “assk”.

I believe that this check can be done with single regexp, but my knowledge about regexp isn’t so deep.

(to get input and show resuls I use php)

Answer 1

Why using a regex here? I don’t see the benefit. What you could do is sort the input string (e.g. both ‘sak’ and ‘ask’ will turn into ‘aks’) and compare that sorted string to a reference string, ‘aks’ in this case. Or just use the same function on the reference string ‘ask’ as well. Something like this:

function str_sort($str) {
    $chars = str_split($str);
    sort($chars);
    return implode('', $chars);
}

$pattern = 'ask';
$input = 'sak';
$valid = str_sort($pattern) == str_sort($input);

echo "Pattern: $pattern;\n";
echo "Input  : $input\n";
echo "Valid  : " . ($valid ? 'yes' : 'no') . "\n";