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<?php $arr1 = array('1', '2', '3', '4', '5', '6', '7'); $arr2 = array('a', 'b', 'c', 'd', 'e'); $count = ceil(count($arr1) / 3) - 1; for ($i = $count - 1; $i >= 0; $i--) { array_splice($arr1, ($i + 1) * 3, 0, $arr2[$i]); } print_r($arr1);

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25.4 ms | 406 KiB | 5 Q