Ruby : Time Math Interview Problem Done Test First

Question from : Blist.com Career Page

  1 # Without using any built in date or time functions, write a function or method
  2 # that accepts two mandatory arguments. The first argument is a string of the
  3 # format "[H]H:MM {AM|PM}" and the second argument is an integer. Assume the
  4 # integer is the number of minutes to add to the string. The return value of
  5 # the function should be a string of the same format as the first argument.
  6 # For example AddMinutes("9:13 AM", 10) would return "9:23 AM". The exercise
  7 # isn't meant to be too hard. I just want to see how you code. Feel free to
  8 # do it procedurally or in an object oriented way, whichever you prefer. Use
  9 # any language you want. Write production quality code. 
 10 # Question Source: http://blist.com/blog/
 11 
 12 # the following solution was developed using TDD
 13 
 14 require 'test/unit'
 15 
 16 class TestTimeCalc < Test::Unit::TestCase
 17 
 18     def setup
 19         @time = "9:13 AM"
 20     end
 21 
 22     def test_new_time_cal
 23         assert_not_nil(TimeCalc.new)
 24     end
 25 
 26     def test_add_minute_zero
 27         assert_equal(@time, TimeCalc.add_minutes(@time, 0))
 28     end
 29 
 30     def test_add_minute_ten
 31         assert_equal("9:23 AM", TimeCalc.add_minutes(@time, 10))
 32     end
 33 
 34     def test_add_minute_thirteen
 35         assert_equal("9:26 AM", TimeCalc.add_minutes(@time, 13))
 36     end
 37 
 38     def test_add_hour
 39         assert_equal("10:13 AM", TimeCalc.add_minutes(@time, 60))
 40     end
 41 
 42     def test_add_two_hours_fifteen_minutes
 43         assert_equal("11:28 AM", TimeCalc.add_minutes(@time, 135))
 44     end
 45 
 46     def test_add_past_meridiem
 47         # 785 minutes = 13 hours and 5 minutes
 48         assert_equal("10:18 PM", TimeCalc.add_minutes(@time, 785))
 49     end
 50 
 51     def test_alpha_hour_min_format_throws_exception
 52         assert_raise(ArgumentError) { TimeCalc.add_minutes("AB:CD AM", 10) }
 53     end
 54 
 55     def test_bad_meridiem_throws_exception
 56         assert_raise(ArgumentError) { TimeCalc.add_minutes("AB:CD TM", 10) }
 57     end
 58 
 59     def test_hr_greater_than_twelve
 60         assert_raise(ArgumentError) { TimeCalc.add_minutes("13:00 PM", 10) }
 61     end
 62 
 63     def test_min_greater_than_fifty_nine
 64         assert_raise(ArgumentError) { TimeCalc.add_minutes("12:60 PM", 10) }
 65     end
 66 
 67 end # end class TestTimeCalc
 68 
 69 class TimeCalc
 70 
 71     def self.add_minutes(time, minutes)
 72       (hour, min, meridiem) = parse_time_string(time)
 73 
 74       hour_increment = (min + minutes)/60
 75       min_increment = (min + minutes)%60 - min
 76       if (hour_increment >= 12)
 77         meridiem = (meridiem == 'AM' ? 'PM' : 'AM')
 78         hour_increment -= 12
 79       end
 80 
 81       hour += hour_increment
 82       min += min_increment
 83 
 84       hour.to_s + ":" + min.to_s + " " + meridiem
 85     end
 86 
 87     private
 88 
 89     def self.parse_time_string(time)
 90         raise ArgumentError unless (matches = time.match(/(\d{1,2}):(\d{1,2})\s+(\w{2})/))
 91         matches = time.match(/^(\d{1,2}):(\d{1,2})\s+([A|P]M)$/)
 92         hour = matches[1].to_i
 93         min = matches[2].to_i
 94         meridiem = matches[3]
 95         raise ArgumentError unless (hour <= 12)
 96         raise ArgumentError unless (min < 60)
 97         return [hour, min, meridiem]
 98     end
 99 
100 end # end class TimeCalc