# assuming all dates are in %dates
use Time::Local;
my %missed = ();
my ($mon, $yr) = split /-/, (sort keys %dates)[0];
my $from = timelocal(1, 0, 0, 1, $mon-1, $yr);
my ($mon, $yr) = split /-/, (sort keys %dates)[-1];
my $to = timelocal(59, 59, 23, 1, $mon-1, $yr);

while ($from < $to){
      @date = localtime($from);
      $date[4]++; $date[5] += 1900; # well, you know...
      # add to %missed if not in %dates
      $missed{"$date[5]-$date[4]"}++ 
              unless exists $dates{"$date[5]-$date[4]"};
      $from += 60*60*24; # add one day
}

print "$_\n" for keys %missed;
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--perlplexer