pete_campbell.rb

require 'time'

TWELVE_HOURS = 12*60*60
TWENTYFOUR_HOURS = TWELVE_HOURS*2

def average_time_of_day(times)

  # Since all times are relative, we don't know if the AM times occur before/after the PM times.
  # We'll make an assumption that all times are somewhat related and thus should occur at about the
  # same time, so we will choose start and end times that create the smallest possible time window.
  # To do this, we will calculate the total time range with the AM times occurring before the PM times,
  # then we'll compare this to the time range when the AM times occur after the PM times.
  #
  # If the AM times occur first, then the time window is the maximum PM time minus the minimum AM time.
  # If the AM times occur after the PM times, then the time window is the maximum AM time plus 24 hours
  # and minus the minimum PM time, eg.
  #
  #  should_we_shift_the_AM_times = ( PM_MAX_TIME - AM_MAX_TIME ) < ( (AM_MIN_TIME+24) - PM_MIN_TIME)
  #
  # Of course, this only applies if we have both AM and PM times....
  
  midnight = Time.parse('12:00am')  # Midnight today, needed since all times are relative

  # Get each time relative to midnight today (since the input times are relative)
  times = times.collect { |t| Time.parse(t)-midnight }  # Convert the original array into relative times
  am_times, pm_times = times.partition { |t| t < TWELVE_HOURS }

  # Adjust any AM times by 24 hours if that makes the total time window smaller
  if ( !am_times.empty? && !pm_times.empty? && (pm_times.max-am_times.min) > (am_times.max-pm_times.min+24*60*60) )
    am_times.each_index { |t| am_times[t] += TWENTYFOUR_HOURS }
    times = pm_times + am_times
  end

  # Uncomment the next line to see the times for the selected shortest time window
  # print "Debug: Time range: #{Time.at(times.min)+midnight.to_i} to #{Time.at(times.max)+midnight.to_i}\n"

  # Calculate the average -  we must add the relative average time to the baseline midnight time so we can
  # get the correct absolute time
  sum = times.inject(0) { |s,i| s+i }
  average_time = Time.at(sum.to_f/times.length)+midnight.to_i # TO_I needed for time addition operator

  average_time.strftime('%I:%M%p').downcase

end