Saari Development

Ali Rizvi's Technical Blog as a Professional Software Development Engineer

Ruby : Time Math Interview Problem With Bug Fixed (still writing test first)

with one comment

While discussing my friend Arsalan’s C# (seemlessly compiled on my linux machine using mcs)
solution and testing it out I found a bug in my own code that. The problem was when adding
more than 12 hours (> 720 minutes) it was not doing the right thing. The code can still be
refactored for cleaner solution but it is too late at night to do that now. Also, my wife
gave me another idea to convert the time to minutes before adding which I will try out later.

# Without using any built in date or time functions, write a function or method
# that accepts two mandatory arguments. The first argument is a string of the
# format “[H]H:MM {AM|PM}” and the second argument is an integer. Assume the
# integer is the number of minutes to add to the string. The return value of
# the function should be a string of the same format as the first argument.
# For example AddMinutes(” AM”,) would return ” AM”. The exercise
# isn’t meant to be too hard. I just want to see how you code. Feel free to
# do it procedurally or in an object oriented way, whichever you prefer. Use
# any language you want. Write production quality code.
# Question Source: http://blist.com/blog/

# the following solution was developed using TDD

require ‘test/unit’

class TestTimeCalc < Test::Unit::TestCase def setup @time = " AM" end def test_new_time_cal assert_not_nil(TimeCalc.new) end def test_add_minute_zero assert_equal(@time, TimeCalc.add_minutes(@time,)) end def test_add_minute_ten assert_equal(" AM", TimeCalc.add_minutes(@time,)) end def test_add_minute_thirteen assert_equal(" AM", TimeCalc.add_minutes(@time,)) end def test_add_hour assert_equal(" AM", TimeCalc.add_minutes(@time,)) end def test_add_two_hours_fifteen_minutes assert_equal(" AM", TimeCalc.add_minutes(@time,)) end def test_add_past_meridiem # minutes = hours and minutes assert_equal(" PM", TimeCalc.add_minutes(@time,)) end def test_alpha_hour_min_format_throws_exception assert_raise(ArgumentError) { TimeCalc.add_minutes("AB:CD AM",) } end def test_bad_meridiem_throws_exception assert_raise(ArgumentError) { TimeCalc.add_minutes("AB:CD TM",) } end def test_hr_greater_than_twelve assert_raise(ArgumentError) { TimeCalc.add_minutes(" PM",) } end def test_min_greater_than_fifty_nine assert_raise(ArgumentError) { TimeCalc.add_minutes(" PM",) } end def test_add_lot_of_minutes # minutes = hours and minutes assert_equal(" AM", TimeCalc.add_minutes(@time,)) end def test_add_up_to_noon # AM plus hr min () assert_equal(" PM", TimeCalc.add_minutes(@time,)) end def test_add_whole_lot_of_minutes # minutes = hours and minutes assert_equal(" AM", TimeCalc.add_minutes(@time,)) end end # end class TestTimeCalc class TimeCalc def self.add_minutes(time, minutes) (hour, min, meridiem) = parse_time_string(time) hour_increment = (min + minutes)/ min_increment = (min + minutes)% - min while (hour + hour_increment >)
meridiem = (meridiem == ‘AM’ ? ‘PM’ : ‘AM’)
hour_increment -=
end

hour += hour_increment
# special case forth hour
meridiem = (meridiem == ‘AM’ ? ‘PM’ : ‘AM’) if hour ==
min += min_increment

hour.to_s + “:” + sprintf(‘%d’, min) + ” ” + meridiem
end

private

def self.parse_time_string(time)
raise ArgumentError unless (matches = time.match(/(\d{,}):(\d{,})\s+(\w{})/))
matches = time.match(/^(\d{,}):(\d{,})\s+([A|P]M)$/)
hour = matches[].to_i
min = matches[].to_i
meridiem = matches[]
raise ArgumentError unless (hour <=) raise ArgumentError unless (min <) return [hour, min, meridiem] end end # end class TimeCalc if __FILE__ == $ puts TimeCalc.add_minutes(ARGV[], ARGV[].to_i) end [/sourcecode]

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Written by imsaar

January 2, 2008 at 9:33 am

Posted in code, ruby

One Response

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  1. If you haven’t looked at it yet, try my updated code at http://softwareworks.wordpress.com

    My design converts time to minutes before performing any arithmetic.

    Arsalan

    January 2, 2008 at 5:23 pm


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