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50 lines
1.7 KiB
Python
50 lines
1.7 KiB
Python
"""How many Sundays fell on the first of the month during the twentieth century?
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You are given the following information, but you may prefer to do some research for yourself.
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* 1 Jan 1900 was a Monday.
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* Thirty days has September,
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April, June and November.
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All the rest have thirty-one,
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Saving February alone,
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Which has twenty-eight, rain or shine.
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And on leap years, twenty-nine.
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* A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
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How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
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"""
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class Day:
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SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY = range(7)
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def is_leap_year(year):
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return (year % 100 > 0 and year % 4 == 0) or (year % 400 == 0)
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def main():
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year = 1900
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# 1/1/1900 was a Monday
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first_day = Day.MONDAY
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total = 0
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while year < 2000:
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year = year + 1
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# Count last year's days to advance the starting weekday
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days = 366 if is_leap_year(year - 1) else 365
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# List the number of days in each month for this year
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months = [
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31,
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29 if is_leap_year(year) else 28,
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31, 30, 31, 30, 31, 31, 30, 31, 30, 31
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]
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first_day = (first_day + days % 7) % 7
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sundays = 0
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for m in range(len(months)):
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days = sum(months[:m])
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first_sunday = (7 - ((first_day + days % 7) % 7)) % 7 + 1
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if first_sunday == 1:
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total = total + 1
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print 'Total months beginning on Sunday from 1/1/1901 to 12/31/2000: {0}'.format(total)
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if __name__ == '__main__':
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main()
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