#!/usr/bin/perl
use strict;

my @temp = qw(2000-4 2000-2 2000-1 2000-12 2001-1 2002-12 1999-12);


my @dates      = (sort {
                       my @a_date = split '-', $a;
                       my @b_date = split '-', $b;
                       $a_date[0] <=> $b_date[0]
                       ||
                       $a_date[1] <=> $b_date[1];
                       } @temp);

my @start_date = split '-', shift @dates;
my @end_date   = split '-', pop @dates;

# use mod 12 to make job easy
my $start_count = $start_date[0]*12 + $start_date[1]-1;
my $end_count   = $end_date[0]*12   + $end_date[1]-1;

# hash of dates in this time
my %date_hash;

# build hash
for ($start_count..$end_count) {
  # here's the sneaky trick :)
  my $year = int($_/12);
  my $month = $_%12 + 1;
  $date_hash{$year}{$month}++;
}

# now delete elements that exist
for (@temp) {
  /(\d+)-(\d+)/;
  delete $date_hash{$1}{$2};
}

# print missing
print "Missing dates are\n\n";
my $count=1;

foreach my $year (sort {$a <=> $b} keys %date_hash) {
  for (sort {$a <=> $b} keys %{$date_hash{$year}}) {
    printf("%4d-%2d  ",$year,$_);
    print "\n" unless $count%4; $count++;
  }
}