How Can I Generate All Combinations of a Specific Size from a Character Set?

Determining All Combinations of Specified Sizes from a Character Set

This inquiry seeks an algorithm capable of generating all potential combinations of a certain size from a given set of characters. Let's delve into a solution using a recursive function:

function sampling($chars, $size, $combinations = array()) {
    if (empty($combinations)) {
        $combinations = $chars;
    }
    if ($size == 1) {
        return $combinations;
    }
    $new_combinations = array();
    foreach ($combinations as $combination) {
        foreach ($chars as $char) {
            $new_combinations[] = $combination . $char;
        }
    }
    return sampling($chars, $size - 1, $new_combinations);
}

Consider an example with $chars = ['a', 'b', 'c']:

$output = sampling($chars, 2);
var_dump($output);

The output displays all possible combinations of size 2:

array(9) {
  [0]=>
  string(2) "aa"
  [1]=>
  string(2) "ab"
  [2]=>
  string(2) "ac"
  [3]=>
  string(2) "ba"
  [4]=>
  string(2) "bb"
  [5]=>
  string(2) "bc"
  [6]=>
  string(2) "ca"
  [7]=>
  string(2) "cb"
  [8]=>
  string(2) "cc"
}

This recursive approach effectively generates all combinations, ensuring that even combinations of sizes larger than the initial set are accommodated.

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