What about just:

my %dates;
for ( @intersect )
{
    my ( $year, $month, $day ) = Add_Delta_Days( 1, 1, 1, $_ - 1 );
    push @{ $dates{$year}->{$month} }, $day;
}
[download]

Then you just have to sort the days.

Update: Looks like Skeeve beat me to it. Nevermind.