use Math::Combinatorics;

my @n = qw(0 1 2 3 4 5 6 7 8 9);
my $combinat = Math::Combinatorics->new(count => 2,
                                          data => [@n],
                                         );

$i = 0;
while(my @permu = $combinat->next_permutation){
    print join('', @permu)."\n" if ($i >= 999999 && $i <= 1000001);
    $i++;
    print "on $i\n" if ($i % 100000 == 0);
    last if ($i > 1000001);
}