olivernn.rb

# 
# This script was written for the ruby learning blog challenge
# http://rubylearning.com/blog/2009/10/08/rpcfn-average-arrival-time-for-a-flight-2/
# 
# The script will calculate the average arrival time from an array of given arrival times.
# It is assumed that the arrival times will be in the format HH:MM and be in the 12hour clock
# format with a 2 digit meridiem. The hours do not need to be padded to fill 2 digits, e.g. 6:51pm is valid
# 
# For the script to work the arrival times MUST be in order, starting with the earliest ever arrival time.
# For cases where arrival times span more than one day it is assumed that the first time is the earliest
# time in a calendar sense.  For example if the flight arrived on Friday at 23:59 and Saturday at 00:01
# then they should be entered into the array as follows ["11:59pm", "12:01am"]
# 
# It is also assumed that 1 minute past midnight would be represented as 12:01am
# 
# Finally, it is assumed that the airline can never be more than 24 hours late

arrival_times = ["11:51pm", "11:56pm", "12:01am", "12:06am", "12:11am"] # put your times in this array

class ArrivalTime
  
  attr_accessor :hours, :minutes, :meridiem, :twelve_hour
  
  def initialize(time)
    @time = time
    @twelve_hour = true
    parse
    convert_to_24hr
  end
  
  def convert_to_24hr
    if meridiem == "pm"
      self.hours = hours + 12
    else
      self.hours = hours - 12 if hours >= 12
    end
    self.twelve_hour = false
  end
  
  def to_sec
    (hours * 3600) + (minutes * 60)
  end
  
  def add_24hrs
    self.hours = hours + 24
  end
  
  private
  
  def parse
    time_array = @time.split(":")
    self.hours = time_array[0].to_i
    self.minutes = time_array[1].to_i
    self.meridiem = time_array[1].gsub(/[0-9]{2}/, "")
  end
end

# monkey patching array so that it can sum and then average the arrival times
class Array
  def sum_times
    inject(0) {|sum, arrival_time| sum + arrival_time.to_sec}
  end
  
  def average
    sum_times / size
  end
end


# start looping through the input arrival times

arrival_times.collect! do |t|
  ArrivalTime.new(t)
end

arrival_times.each_with_index do |time, i|
  unless i == 0
    if time.hours < arrival_times[i-1].hours
      time.add_24hrs
    end
  end
end

average_arrival_time = Time.at(arrival_times.average - 3600) # since epoch was at 01:00 we need to take away an hour

puts "The average arrival time is " + average_arrival_time.strftime("%I:%M%p")