<?php
$currentValues = [1, 2];
$newValues = [1, 3, 1, 4, 2];
$a = array();
$checkValues = array_flip($currentValues);
foreach($newValues as $v){
if(!isset($checkValues[$v])){
$a[] = $v;
}
}
print_r($a);
PD9waHAKCiRjdXJyZW50VmFsdWVzID0gWzEsIDJdOwokbmV3VmFsdWVzID0gWzEsIDMsIDEsIDQsIDJdOwokYSA9IGFycmF5KCk7CiRjaGVja1ZhbHVlcyA9IGFycmF5X2ZsaXAoJGN1cnJlbnRWYWx1ZXMpOwpmb3JlYWNoKCRuZXdWYWx1ZXMgYXMgJHYpewoJaWYoIWlzc2V0KCRjaGVja1ZhbHVlc1skdl0pKXsKCQkkYVtdID0gJHY7Cgl9Cn0KcHJpbnRfcigkYSk7