ruby_challenge_2.rb

require 'time'

# define the regular arrival time, that is used to detect a cycle
REGULAR_ARRIVAL_TIME = "10:00pm"

# maximum delay can be 23 hours 59 minutes (because of cycling times)
def average_time_of_day(arrivals)
  # check for a cycle and convert arrival times into UNIX timestamps
  arrivals.collect!{ |a|
                    a = Time.parse(a)
                    a += 60*60*24 if a < Time.parse(REGULAR_ARRIVAL_TIME)
                    a.to_i
                }
  # get the average timestamp
  sum = arrivals.inject{ |sum,x| sum + x }
  average_time = sum/arrivals.length
  # convert the timestamp back and return it
  average_time = Time.at(average_time)
  
  average_time.strftime("%I:%M%p")
end