title: Get total number of ranges of a given length in an array
body: <p>I have an array <code>total</code> of 12 elements, each element represents and int.  For instance <code>total[0] = 1</code>.   I have another array <code>remaining</code> that is <code>total</code> - <code>occupied spaces</code>.  <code>remaining</code> will have fewer elements that <code>total</code>.</p>
  
  <p>I want to write a method that can look in <code>total</code> for instances where there are >= <code>size</code> gaps between consecutive ints in the array.  For example:</p>
  
  <pre><code>If `foo.total = [1,2,6,7,8,9,]`
  then when I call `foo.number_of_slots_available(3)`
  I get `2` (because 3,4,5 is not included and 10,11,12 is not included)
  </code></pre>
  
  <p>Here are the beginnings of my method:</p>
  
  <pre><code>def number_of_slots(size)
    total_array = (1..12).to_a
    occupied_spaces = some_map.to_a
    remaining_array = total_array - occupied_spaces
    return ????
  end 
  </code></pre>