Solution to RPCFN #2

average_time_of_day.rb

module AverageTimeOfDay
  require 'date'
  # Assumes times_of_day is an array of valid time strings in chronological
  # order.
  def average_time_of_day(times_of_day)
    # Convert times_of_day to an array of Time objects, ensuring that times
    # are in chronological order by adding a day if the the time of the
    # current iteration is earlier than the last iterated time.
    times = times_of_day.inject([]) do |times, time_of_day|
      dt    = DateTime.strptime(time_of_day, "%I:%M%p")
      time  = Time.local( dt.year, dt.month, dt.day, dt.hour, dt.min )
      time += ( 60 * 60 * 24 ) if times.last && times.last > time
      times.push(time)
    end

    # Compute the average time
    average_time = times.inject(0) {|m,t| m + t.to_i } / times.size

    # Format the average time
    Time.at(average_time).strftime("%I:%M%p").downcase.gsub(/^0/, '')
  end
end


# Execute tests if this file is run by itself.
if $0 == __FILE__
  require "test/unit"
  include AverageTimeOfDay
 
  class TestAverageTimeOfDay < Test::Unit::TestCase
    def test_average_time_of_day
      assert_equal "12:01am", average_time_of_day(
        ["11:51pm", "11:56pm", "12:01am", "12:06am", "12:11am"] )

      assert_equal "6:51am", average_time_of_day(
        ["6:41am", "6:51am", "7:01am"] )
    end
  end
end