#!/usr/bin/perl

use strict;
use warnings;

my @in = (1 .. 12);
my @out = reverse @in[$#in / 2 + 1 .. $#in];

splice @out, $_ * 2 - (($_ % 2) ? 1 : 2), 0, $_ for (@in[0 .. $#in / 2
+]);

print "in: \t@in\n";
print "out: \t@out\n";
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bye

update 1: corrected the code and added the output