use strict;
use warnings;

use Data::Dumper;

my (%ha, %hb);

my @a = (1,2,3,4,5,6); 
my @b = (4,5,6,7,8,9); 

@ha{@a} = (1) x @a;
@hb{@b} = (1) x @b;

my @diff = ( (map { ['<', $_] } grep { !($hb{$_}) } @a),
             (map { ['>', $_] } grep { !($ha{$_}) } @b) );


print Dumper (\@diff);