$ git clone https://github.com/bradleypallen/doomsday.git
$ cd doomsday
$ chmod +x *.py

$ ./doomsday.py
Type 'q' to quit, 0 - 6 to enter the day of the week.
February 8th, 1858? 6
Wrong! February 8th, 1858 fell on a Monday.
1) Calculate the anchor day for the 19th century.
doomcentury = ((5*19 + floor(18/4)) mod 7 + Thursday) mod 7
            = ((95 + 4) mod 7 + Thursday) mod 7
            = (99 mod 7 + 4) mod 7
            = (1 + 4) mod 7
            = 5 mod 7
            = 5
2) Calculate the doomsyear for year 58 in the century.
doomsyear   = 7's complement of ((58/2)+11 mod 7)
            = 7's complement of (40 mod 7)
            = 7's complement of 5
            = 2
3) Calculate the doomsmonth for February of the year.
1858 was not a leap year, so February 21st, 1858 fell on a Doomsday.
doomsmonth  = 8 - 21
            = -13
4) Calculate the day of the week.
day of week = (doomscentury + doomsyear + doomsmonth) mod 7
            = (5 + 2 + -13) mod 7
            = -6 mod 7
            = 7's complement of (6 mod 7)
            = 7's complement of 6
            = 1
            = Monday
August 29th, 2129? 1
Correct! August 29th, 2129 falls on a Monday.
March 9th, 2580? q
Accuracy = 50% over 2 trials