title: Missing Date Ranges
body: <p>I need to find all the missing date ranges from the rest of the year given a collection of date ranges. All the date ranges fall within the same year. And there are no overlaps between the date ranges.</p>
  
  <p>eg: [(1/31/2011 - 5/1/2011), (6/5/2011 - 12/1/2011)] is available in Collection
  then teh missing date ranges are [(1/1/2011 - 1/30/2011) , (5/2/2011 - 6/4/2011) ,(12/2/2011-12/31/2011)]</p>
  
  <p>What would be an efficient way to solve this problem? </p>