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solve19.py
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solve19.py
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# https://projecteuler.net/problem=19
# Run with: 'python solve19.py'
# using Python 3.6.9
# by Zack Sargent
# Prompt:
# You are given the following information,
# but you may prefer to do some research for yourself.
# 1 Jan 1900 was a Monday.
# Thirty days has September,
# April, June and November.
# All the rest have thirty-one,
# Saving February alone,
# Which has twenty-eight, rain or shine.
# And on leap years, twenty-nine.
# A leap year occurs on any year evenly divisible by 4,
# but not on a century unless it is divisible by 400.
# How many Sundays fell on the first of the month during
# the twentieth century (1 Jan 1901 to 31 Dec 2000)?
month_to_days = {
1: 31, # January
2: None, # February
3: 31, # March
4: 30, # April
5: 31, # May
6: 30, # June
7: 31, # July
8: 31, # August
9: 30, # September
10: 31, # October
11: 30, # November
12: 31, # December
}
class Week:
# day = 0..6, Monday to Sunday
def __init__(self):
self.day = -1
def is_sunday(self) -> bool:
return self.day == 6
def next_day(self):
if self.day < 6:
self.day += 1
else:
self.day = 0
def get_days(month: int) -> int:
if month == 2: # February
if year % 100 != 0 or year % 400 == 0:
if year % 4 == 0:
return 29
return 28
else:
return month_to_days[month]
week = Week()
sundays = 0
for year in range(1900, 2000 + 1):
for month in range(1, 12 + 1):
days = get_days(month)
for day in range(1, days + 1):
week.next_day()
if year >= 1901:
if day == 1 and week.is_sunday():
sundays += 1
print(sundays)
# -> 171