Recycle calendars

Many years share their structure in such a way as to be able to use the same calendar.
For example in 2012 you can use a calendar or diary designed for 1984. Here is a short script to find out which years this is valid for.

Dictionary<string,List<int>> similarYears = new Dictionary<string,List<int>>();

for(int year = DateTime.MinValue.Year; year <= DateTime.MaxValue.Year; year++)

{

DateTime Jan1 = new DateTime(year, 1, 1);

DateTime Dec31 = new DateTime(year, 12, 31);

string key = Jan1.DayOfWeek.ToString() + ":" + Dec31.DayOfWeek.ToString();

if (!similarYears.ContainsKey(key))

similarYears[key] = new List<int>();

similarYears[key].Add(year);

}