my %url;
my $nested = 0;
my $MAX_DEPTH = 3;

my @links = getlinks($FIRST_URL);
savelinks('.', @links);

sub savelinks {
    my $parent = shift;
    $nested++;
    for my $link (@_) {
        $url{$link} = $parent unless(exists($url{$link}));
        if($nested <= $MAX_DEPTH) {
            my @links = getlinks($link);
            savelinks($link, @links);
        }    
    }
}