What would be the closest order approximation runtime for the following pseudocode segment in terms of $N($initial size of unused$),$ assume removal and insertion is $O(1)$

fun$($unused$,$ arr$)\{$

if unused size is $0\{$

return

$\}$

Let value be first in unused

remove value from unused

fun$($unused$,$ arr$)$

insert value into arr

fun$($unused$,$ arr$)$

remove value from arr

insert value into unused

$\}$

$(N^N)$

$(N^2)$

$(2^N)$

$(1)$

$(N)$

$(N!)$