What about something like... 
my $error = 0;
my @tmp = sort datesort qw( 2000-4 2000-2 2000-1 2000-12 2001-1 2002-1
+2 1999-12 );
my($year,$month) = split '-', $tmp[0];
for(my $i = 1; $i < @tmp; $i++) {
  if(++$month == 13) {
    $month = 1;
    $year++;
  }
  if($tmp[$i] ne "$year-$month") {
    print "ERROR! gap at '$year-$month', '$tmp[$i]' found!\n";
    $error = 1;
    last;
  }
}
print "Success\n" unless $error;
sub datesort {
  my($a1,$a2) = split '-', $a;
  my($b1,$b2) = split '-', $b;
  $a1 <=> $b1 or $a2 <=> $b2;
}

[download]
Tested on the bad and good arrays, you should be able to modify it for your needs easily enough...

it would be shorter if your dates were zero padded.

Update on afterthought I should say what it does... it sorts the date array (could be an array of hash keys), it then starts at the first, or earliest one, it goes through the array adding one to the month and wrapping the year and setting month to 1 if the month hits 13. it goes till it finds a date it didnt expect, or gets to the end of the array sucessfully. Pretty simple, needed the special sort since months were not zero padded.
                - Ant

In reply to Re: Finding gaps in date ranges by suaveant
in thread Finding gaps in date ranges by Ovid

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.