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<?php $a = [1, 2, 3, 4, 3, 2, 1]; $j = count($a) - 1; $output = []; for($i = 0; $i > count($a); $i++) { if ($a[i] !== $a[j]) { $output = $a[i]; } $j--; } print_r($output);

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13.8 ms | 407 KiB | 5 Q