Python based Solution to Project Euler Problem 19

project-euler-19.py

# 1 Jan 1901 to 31 Dec 2000
# 1 Jan 1900 Monday => 1 Jan 1901 => Tuesday
month_days = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

def is_leap(y):
	return y % 400 == 0 if y % 100 == 0 else y % 4 == 0

def get_month_days(y, i):
	if is_leap(y) and i == 1:
		return 29
	return month_days[i]

def get_good_sundays(year):
	res = 0
	diff_years = year - 1900
	leap_years = 0 if (diff_years <= 4 or diff_years == 100) else diff_years / 4
	odd_days = diff_years + leap_years

	curr = 1 + odd_days

	for i in range(0, 12):
		if i != 0:
			curr += get_month_days(year, i-1)
		curr %= 7

		if curr == 0:
			res += 1

	return res


ans = 0

YEAR_START = 1901
YEAR_END = 2000

for y in range(YEAR_START, YEAR_END+1):
	ans += get_good_sundays(y)

print(ans)