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<?php $myArray = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o"]; for($i = 0; $i < count($myArray); $i += 5) { array_splice($myArray, $i, 0, 1); } print_r($myArray);

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38.56 ms | 405 KiB | 5 Q