I like Bill's reply

here is another way. I'm assuming there are no collisions among the 2nd level keys. I also assume that the 2nd level keys are non-negative integers and are not large numbers. I also note that you don't use the 1st level keys.

use strict;
use warnings;

my $VAR1 = {
          '315' => {'8' => 0},
          '329' => {'6' => 0},
          '352' => {'5' => 0},
          '390' => {'1' => 0},
          '280' => {'7' => 1},
          '360' => {'9' => 0},
          '349' => {'4' => 0},
          '305' => {'10' => 0},
          '380' => {'3' => 1},
          '251' => {'2' => 0}
};

my @a;
for my $x (values %$VAR1 ) {
    for my $y ( keys %$x ) {
        $a[$y]  = [$y, $x->{$y}];
    }
}
print join("\t", ( map { $_->[0]; }  grep { defined } @a ) ), "\n";
print join("\t", ( map { $_->[1]; }  grep { defined } @a ) ), "\n";
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