Question

i need to calculate the number of workdays between two dates. a workday is any day between Monday through Friday except for holidays. the code below does this, but it uses a loop. does anyone see a way to get rid of the loop or at least optimize it?

thanks
konstantin

using System;
using System.Linq;

namespace consapp
{
    static class Program
    {
        static void Main(string[] args)
        {
            var holidays = new DateTime[] { new DateTime(2010, 11, 23), new DateTime(2010, 11, 30) };

            var date_start = new DateTime(2010, 12, 3);
            var date_end = date_start.AddDays(-9.9);
            var duration = (date_end - date_start).Duration();

            for (var d = date_end; d < date_start; d = d.Date.AddDays(1))
            {
                if (holidays.Contains(d.Date) || d.DayOfWeek == DayOfWeek.Saturday || d.DayOfWeek == DayOfWeek.Sunday)
                {
                    duration -= TimeSpan.FromDays(1) - d.TimeOfDay;
                }
            }
            Console.WriteLine(duration);
        }
    }
}

Answer 1

I would investigate an algorithm like the following. (Sorry no code provided.)

1. Count the number of full 7-day weeks between your start and end date. You should be able to do this with .NET DateTime and TimeSpan objects.
2. For each full 7-day week, add 5 days to your result.
3. Figure out the partial weeks including your start and end dates.
4. Loop through your holidays and reduce your result by 1 for each holiday between your start and end date. Looping is better here because there are likely far fewer holidays to loop over than days between your start and end date.

Have fun!

EDIT: For source code, check out this answer: Calculate the number of business days between two dates?