refactored based on challenge feedback (unit test, inject, and strfmtime)

tomv.rb

# Ruby Programming Challenge For Newbies, (#2)
# Author: tomv
# 
# Calculate the average time of day from several times in the format
#  [ '12:11am', '11:51pm','11:56pm','12:01am', '12:06am']
# returns the average time in string format
# => '12:01am'
# My approach was to get the average difference between each of the
# times, compared to the first time in the list.
# Then add the average difference in time to the base time to get an average.
# The trick was to figure out how to minimize the differences by moving the day around
#  since for the edge cases, the next day (12:01 pm) or the previous day (11:55am)
#  might yeild a smaller difference that the same time on the same day.

# Would be easy to extend this to get a standard deviation of the time differences, so you could
# Likely arrival is  "12:30pm +/- 12 minutes in most cases, or something.
#
# I included a simple set of tests as an additional function: test_average_time_of_day()
#  that runs through a few test cases.
#  Note that the results for average_time_of_day(['12am', '12pm']) could be either '6pm' or '6am'

require 'time'


# To run in irb
#   >load 'tomv.rb'
#   >average_time_of_day([ '12:11am', '11:51pm','11:56pm','12:01am', '12:06am'])
#  => "12:01am"
def average_time_of_day(times)
  total  = 0.0
  base_time = Time.parse(times[0]) #take the first time, and use as a 'base' then calculate avg. difference.
  times.each do |t|
    simple_time = Time.parse(t)                      # Time.parse assumes current day when parsing
    d1 = base_time - simple_time                     # Get the time difference between base and current item's time for same day
    prev_next = (base_time.hour > 12)? 1:-1          # Get diff between base and next or prev day.(next day for pm, prev day for am times)
    d2 = base_time - (simple_time + 86400*prev_next) # use next day time
    diff = (d1.abs < d2.abs)? d1: d2                 # select the smallest difference
    total += diff                                    # running total of differences used for calc. avg. difference from base.
  end
  # calcuate average time by adding avg. difference of times to the base time, then format
  (base_time - (total/times.size)).strftime('%l:%M%P')
end



# Simple test of function
# Run the function through it's paces with a few simple tests
def test_average_time_of_day 
  test=[]

  test[0] = {
    :description => 'Initial Challenge Example',
    :input_times => [ '12:11am', '11:51pm','11:56pm','12:01am', '12:06am'],
    :correct_answer => '12:01am'
  }

  test[1] = {
    :description => 'Additional provided example',
    :input_times => ['6:41am','6:51am','7:01am'],
    :correct_answer => '6:51am'
  }

  test[2] = {
    :description => 'Edge case: 12am and 12pm (6am or 6pm are correct)',
    :input_times => ['12am','12pm'],
    :correct_answer => '6:00pm'
  }

  test[3] = {
    :description => 'Edge case: times around noon time ( AM to PM)',
    :input_times => ['11:45am','12:15pm','11:50am', '12:10pm' ],
    :correct_answer => '12:00pm'
  }

  test[4] = {
    :description => 'Simple case with several entries',
    :input_times => ['7:15am','7:30am', '7:45am', '7:30am', '7:30am', '7:45am','7:15am'],
    :correct_answer => '7:30am'
  }

  test.each do |item|
    puts "Test: #{item[:description]} "
    puts "Input times: #{item[:input_times].inspect}"
    puts "Expected: #{item[:correct_answer]}"
    puts "Got:      #{average_time_of_day(item[:input_times])}"

    success = average_time_of_day(item[:input_times]).strip == item[:correct_answer].strip
    if success
      puts '=========== PASSED =============='
    else
      puts '########### FAILED ##############'

    end
    puts '---------------------------------------------'
  end
 puts "All Done"
end