use strict;
use warnings;

use Test::More no_plan => 1;

my @input = (
    [ 'a' .. 'f' ],
    [ 'g' .. 'l' ],
    [ 'm' .. 'r' ],
    [ 's' .. 'x' ],
);

my @expected = split '', 'abcdeflrxwvutsmghijkqpon';

my @try;
while (@input) {
    push @try, @{shift @input};
    push @try, pop @$_ for @input;
    @input = reverse @input;
    @$_ = reverse @$_ for @input;
}

print "@expected\n";
print "@try\n";

is_deeply( \@try, \@expected );