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<?php $input = "1;2;3;4;5;6;7;8;9"; $n = 2; echo implode(';', array_merge(array_slice($arr = explode(';', $input), -$n), array_slice($arr, $n, -$n), array_slice($arr, 0, $n)));

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63.01 ms | 402 KiB | 5 Q