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<?php function count_and_find($arr) { sort($arr); $missing = array(); $index = 0; $count = count($arr); while ($num = array_shift($arr)) { do { if ($index < $num) { $missing[] = $index; $index++; } } while ($index < $num); } return array('missing' => $missing, 'total' => $count); } var_dump(count_and_find(array(1,6,2,9,3,0,5,7,4)));

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45.02 ms | 402 KiB | 5 Q