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<?php $arr = [10, 20, 20, 10, 10, 30, 50, 10, 20]; $n = 9; $temp = array_count_values($arr); // count number of occurences $e = array_reduce($temp, function ($carry, $item) { $carry += ($item > 1 ? intval($item / 2) : 0); return $carry; }); echo $e;die;

preferences:
32.82 ms | 405 KiB | 5 Q