robisonsantos.rb

#!/usr/bin/ruby -w

# Robison WR Santos
# Brazil
# rwrsantos@gmail.com
#
# This method calculates the average time given a list with all time values
# you want the count.
# It assumes that the first value on the list is the lesser value of it.
# By this assumption, it treats this value as the base to do all the computation 
# and find the most probable average time of the passed list.

# How many seconds do we have in one day?
A_DAY = 24 * 60 * 60

def average_time_of_day(times_str)
  # transforms all str_time into float time representation and store them into
  # an array
  times = times_str.map {|t| Time.parse(t).to_f}
  
  # get the first element as a basis
  base_time = times.delete_at(0)
 
  # get all deltas between the current t time and the base time
  # as Time.parse assumes the time from today, if the current time is lesser than
  # the base time, we assume that it comes from the next day.
  deltas = times.map {|t| t >= base_time ? t - base_time : (t + A_DAY) - base_time}
  
  # sum all the deltas
  deltas_sum = deltas.inject(0) {|s,d| s + d}
  
  # calculate the average delta
  average_delta = deltas_sum / (times.size + 1)
  
  # calculate the average time by the sum of the average_delta and the base_time
  Time.at(base_time + average_delta).strftime("%I:%M%p")
end

# tests
require 'test/unit'

class TestAverageTimeOfDay < Test::Unit::TestCase
    
  def test_five_values_on_the_same_range
    times_str = ['11:50pm','11:52pm','11:54pm','11:56pm','11:58pm']
    assert_equal '11:54PM', average_time_of_day(times_str)
  end
  
  def test_four_values_on_the_same_range
    times_str = ['11:50pm','11:52pm','11:54pm','11:56pm']
    assert_equal '11:53PM', average_time_of_day(times_str)
  end
  
  def test_time_passes_from_midnight
    times_str = ['11:51pm','11:56pm','12:01am','12:06am','12:11am']
    assert_equal '12:01AM', average_time_of_day(times_str)
  end
  
  def test_time_passes_from_noon
    times_str = ['11:51am','11:56am','12:01pm','12:06pm','12:11pm']
    assert_equal '12:01PM', average_time_of_day(times_str)
  end
  
  def test_three_value_on_the_same_range
    times_str = ['6:41am','6:51am','7:01am']
    assert_equal '06:51AM', average_time_of_day(times_str)
  end
  
  def test_only_one_value_in_the_morning
    times_str = ['6:41am']
    assert_equal '06:41AM', average_time_of_day(times_str)
  end
  
  def test_only_one_value_in_the_afternoon
    times_str = ['6:41pm']
    assert_equal '06:41PM', average_time_of_day(times_str)
  end
  
  def test_twelve_hours_different_from_morning
    times_str = ['6:41am','6:41pm']
    assert_equal '12:41PM', average_time_of_day(times_str)
  end
  
  def test_twelve_hours_different_from_afternoon
    times_str = ['6:41pm','6:41am']
    assert_equal '12:41AM', average_time_of_day(times_str)
  end
  
  def test_mixed_time_post_midnight_with_the_lesser_value_before_midnight
    times_str = ['11:10pm','11:15pm','12:03am','11:30pm','11:48pm']
    assert_equal '11:33PM', average_time_of_day(times_str)
  end
  
  def test_mixed_time_post_midnight_with_the_lesser_value_after_midnight
    times_str = ['12:03am','11:10pm','11:15pm','11:30pm','11:48pm']
    assert_equal '06:45PM', average_time_of_day(times_str)
  end
  
  def test_all_values_the_same
    times_str = ['11:10pm','11:10pm','11:10pm','11:10pm','11:10pm']
    assert_equal '11:10PM', average_time_of_day(times_str)
  end
end