[PYTHON] Project Euler 19

problem

The following information is given.

January 1, 1900 is Monday. September, April, June, and November have up to 30 days, and all months except February have up to 31 days. February has 28 days, but in leap years it is 29 days. A leap year occurs in a year when the Christian era is divisible by 4. However, a year when the Christian era is not divisible by 400 and divisible by 100 is not a leap year. How often does the beginning of the month be Sunday during the 20th century (January 1, 1901-December 31, 2000)? http://odz.sakura.ne.jp/projecteuler/index.php?cmd=read&page=Problem%2019

Answer

Sunday: 0 Monday: 1 Tuesday: 2 Wednesday: 3 Thursday: 4 Friday: 5 Saturday: 6 And. The next date of the first day of the next month can be calculated from the day of the week date of the first day of the previous month and the number of days of the previous month by the following formula. (7 is the number of days of the week). Using this, I wrote the following code.

nextdate = (date+days) % 7

# -*- coding: utf-8 -*-
def getdays(month, year):
  if month in [1,3,5,7,8,10,12]:
    return 31
  elif month in [4,6,9,11]:
    return 30
  elif year%400 == 0:
    return 29
  elif year%100 == 0:
    return 28
  elif year%4 == 0:
    return 29
  else:
    return 28

def nextdate(date, month, year):
   return (date + getdays(month, year)) % 7

def nextmonth(month, year):
   if month == 12:
      #December to the next year
      return (1, year+1)
   else:
      return (month+1, year)

def main():
  STARTYEAR = 1901
  LASTYEAR = 2000
  (date, month, year) = (1, 1, 1900)
  ans = 0

  while year <= LASTYEAR:

    #Last month date,month,year to next month date(Day of the week)Get
    date = nextdate(date, month, year)

    #month,Increment year
    (month,year) = nextmonth(month, year)

    #year is in range and date is 0(Sunday)Then add 1 to ans.
    if STARTYEAR <= year <= LASTYEAR and date == 0:
      ans += 1

  print ans

main()