Count number of Mondays in a given date range

Question

Given a date range, I need to know how many Mondays (or Tuesdays, Wednesdays, etc) are in that range.

I am currently working in C#.

Answer 1

Here's some pseudocode:

DifferenceInDays(Start, End) / 7   // Integer division discarding remainder
+ 1 if DayOfWeek(Start) <= DayImLookingFor
+ 1 if DayOfWeek(End)   >= DayImLookingFor
- 1

Where DifferenceInDays returns End - Start in days, and DayOfWeek returns the day of the week as an integer. It doesn't really matter what mapping DayOfWeek uses, as long as it is increasing and matches up with DayImLookingFor.

Note that this algorithm assumes the date range is inclusive. If End should not be part of the range, you'll have to adjust the algorithm slightly.

Translating to C# is left as an exercise for the reader.