Cryptarithm with PHP (basic)

cryptarithm.php

<?php

$first_crypt = "AB";
$second_crypt = "AB";
$result_crypt = "BCC";

function calc($first_crypt, $second_crypt, $result_crypt, $operator = 'add') {
    $crypt_input = str_split($first_crypt . $second_crypt . $result_crypt);
    $merge_input = array_unique($crypt_input);
    sort($merge_input);
    $len_input = strlen(implode("", $merge_input));

    $result_final = "";
    $first_loop = pow(10, $len_input-1);
    $last_loop = pow(10, $len_input);
    for ($i = $first_loop ; $i < $last_loop; $i++) {
        $number_string = (string) $i;
        $split_number_strings = str_split($number_string);
        $number_arrays = array_map('intval', $split_number_strings);
        $key = 0;
        $new_array = [];
        foreach ($merge_input as $char_crypt) {
            if (isset($number_arrays[$key])){
                $new_array[$char_crypt] = $number_arrays[$key];
            } else {
                $new_array[$char_crypt] = 'X';
            }
            $key++;
        }
        $first_calc = convertStringToNumber($first_crypt, $new_array);
        $second_calc = convertStringToNumber($second_crypt, $new_array);
        $result_calc = convertStringToNumber($result_crypt, $new_array);

        switch ($operator) {
            case 'add':
                if ($first_calc + $second_calc == $result_calc && $first_calc != 0 && $second_calc != 0){
                    $result_final .= $first_calc ."<br />";
                    $result_final .= $second_calc ."<br /><hr />";
                    $result_final .= $result_calc ."<br /><br /><br />";
                }
                break;
            
            default:
                $result_final .= "Not Operator Found !";
                break;
        }
    }

    if ($result_final == ""){
        $result_final = "Tidak Ada Solusi untuk Soal ini";
    }
    return $result_final;
}

function convertStringToNumber($string, $list) {
    $splits = str_split($string);
    if (is_array($list) && count($list) > 0 && count($splits) > 0){
        foreach ($splits as $char_original) {
            // echo "c{$char}v{$value}";
            $replace_value = "0";
            if (isset($list[$char_original])){
                $replace_value = $list[$char_original];
            }
            $result = str_replace($char_original, $replace_value, $string);
            $string = $result;
        }
    }
    return (int) $string;
}

echo calc($first_crypt, $second_crypt, $result_crypt);

?>