my $ranges = [
               { I => 2 },
               { I => 3, J => 2 },
               { I => 4, J => 3, K => 2 },
               { I => 5, J => 4, K => 3, L => 2 }
             ];

for my $h ( @$ranges ) {
    my $array = 'NETLIST';
    for my $k (reverse sort keys %$h ) {
        my $a;
        $a->[$h->{$k}] = $array;
        $array = $a;
    }
    # ...
    print Dumper $array;
}