better way to effectively iterate one array over another: http://www.ruby-doc.org/core-2.0/Array.html#method-i-26

ranges_overlap_sum.rb

def sum_of_intersection?(x1, x2, y1, y2)
 intersection = (x1..x2).to_a & (y1..y2).to_a
 intersection.inject{|sum,i| sum + i}
end

p sum_of_intersection?(5,15,10,20)

Pretty cool Matt! Love the set intersection operator. One disadvantage to this approach vs how we talked about earlier (where we manually found the intersecting range) is that if one of our ranges were say a billion numbers wide or more, this code would take up a ton of memory due to having to convert the entire range into an array. You can never run out of cool Ruby shortcuts :)