PHP: Regex, must contain all letters from list - php

Question

Does anyone know how to write regex pattern, that does this:
let's say I have letters in array like
$letters = array('a','b','a');
and also we have a word Alabama and I want preg_match to return true, since it contains letter A two times and B. But it should return false on word Ab, because there aren't two A in that word.
Any ideas ?
EDIT: the only pattern I tried was [a,b,a] but it returns true on every word that does contain one of these letters and also doesn't check it for multiple letter occurences

Answer 1

I think you don't have to overcomplicate the process. You can traverse the letters and check if the exists in the word, if all the letter are there, return true. Something like this:
$letters = array('a','b','a');
$word = "Alabama";
function inWord($l,$w){
//For each letter
foreach($l as $letter){
//check if the letter is in the word
if(($p = stripos($w,$letter)) === FALSE)
//if false, return false
return FALSE;
else
//if the letter is there, remove it and move to the next one
$w = substr_replace($w,'',$p,1);
}
//If it found all the letters, return true
return TRUE;
}
And use it like this: inWord($letters,$word);
Please note this is case insensitive, if you need it case sensitive replace stripos by strpos

Answer 2

Must you need to use regular expressions? Even if the problem can be solved through them, the code will be very complicated.
"Manual" solution will be clearer and takes linear time:
function stringContainsAllCharacters(string $str, array $chars): bool
{
$actualCharCounts = array_count_values(str_split($str));
$requiredCharCounts = array_count_values($chars);
foreach ($requiredCharCounts as $char => $count) {
if (!array_key_exists($char, $actualCharCounts) || $actualCharCounts[$char] < $count) {
return false;
}
}
return true;
}