intervals.rb

class Interval
  attr_accessor :start, :end
  def initialize(start, _end)
    @start = start
    @end = _end
  end
end

def uncovered(intervals)
  sorted = intervals.sort_by {|i| i.start}
  results = [sorted.first]
  sorted.each_cons(2) { |x, y|
    target = results[-1]
    results << y if not y.start.between?(target.start, target.end)
    results[-1].end = y.end if not y.end.between?(target.start, target.end)
  }
  uncovered = []
  results.inject { |x, y|
    uncovered << Interval.new(x.end, y.start)
    y
  }
  uncovered
end

def main
  intervals = [Interval.new(2, 6), Interval.new(9, 12), Interval.new(8, 9), Interval.new(18, 21), Interval.new(4, 7), Interval.new(10, 11)]
  uncovered(intervals).each { |interval| p "#{interval.start}, #{interval.end}" }
end