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run code in 300+ PHP versions simultaneously
<?php $array=[[8,9,7],[7,8,9,33,21],[11,12,33,21,9,31]]; $unique=preg_match_all('~\b(\d+)\b(?!.*\b\1\b)~',json_encode($array),$out)?$out[0]:[]; sort($unique); var_export($unique);

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