New Syllabus

Calendar problem revisited

January 3rd, 2008   Posted by John in assignments, cs1 Here’s a twist on the classic “What day of the week does a particular date fall on?” problem. A programming solution using the following approach would use several simple lookup tables, probably implemented as arrays, lists, or hash maps. I’ve translated the basic idea that I found here (via reddit) into something more appropriate for programming instructors and students.The result can be calculated using the following formula:dayOfWeek = (yearCode + monthCode + day) % 7The result is an integer in the range 0 to 6, interpreted as follows:

Result	Day
0	Saturday
1	Sunday
2	Monday
3	Tuesday
4	Wednesday
5	Thursday
6	Friday

As usual, leap year needs to be accounted for. If the date in question is in a leap year, the result should be decremented by one for the months of January and February.The month code is a non-intuitive integer as follows:

Month	Code
January	1
February	4
March	4
April	0
May	2
June	5
July	0
August	3
September	6
October	1
November	4
December	6

The year code can also be determined using a lookup table, such as:

Year	Code
2005	5
2006	6
2007	0
2008	2
2009	3
2010	4

Or the year code can be computed using the following formula:yearCode = (centuryCode + twoDigitYear + (twoDigitYear / 4)) % 7The two digit year value is the last two digits of the year (84 for 1984). The century code follows the 6-4-2-0 pattern below and applies only to dates in theGregorian calendar.

Century	Code
1600s	6
1700s	4
1800s	2
1900s	0
2000s	6
2100s	4
2200s	2
2300s	0

Happy programming.