When You need to calculate integer ranges

ranges.rb

def ranges(array_of_hours)
  ranges = array_of_hours.map do |hour|
    (hour..hour)
  end
  ranges = ranges.sort_by {|r| r.first }
  *outages = ranges.shift
  ranges.each do |r|
    lastr = outages[-1]
    if lastr.last >= r.first - 1
      outages[-1] = lastr.first..[r.last, lastr.last].max
    else
      outages.push(r)
    end
  end
  outages
end


result = ranges([1, 2, 3, 4, 6, 8, 9]).join(',')

if result == '1-4,6,8-9'
  puts "Congratulations"
else
  puts result
end