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<?php $levels = [4=>40]; $a = array_keys($levels); sort($a); $max = end($a); $toAdd = array_diff(array_keys(array_fill(1, $max, 0)), $a); $result = array_fill_keys($toAdd, 0); $merged = $levels + $result; ksort($merged); var_dump($merged);

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53.92 ms | 402 KiB | 5 Q