38 lines
1.0 KiB
Python
38 lines
1.0 KiB
Python
#Counting Sundays
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#Problem 19
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#
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#You are given the following information, but you may prefer to do some
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#research for yourself.
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#
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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
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# unless it is divisible by 400.
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#
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#How many Sundays fell on the first of the month during the twentieth century
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#(1 Jan 1901 to 31 Dec 2000)?
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#
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# let's encode sunday 0 - mon 1 ...
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# 1 Jan 1901
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a = 365 #1900 is not a leap year
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a += 1 #1 jan is monday
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a %= 7 #the day of 1 jan 1901
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c = 0 #count of months for which sundays fell on march.
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m = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]
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for i in range( 1901, 2001 ):
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for j in range( 1, 13 ):
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if a==0:
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c += 1
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a += m[j-1]
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if j==2 and i%4==0:
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a += 1
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a %= 7
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print(c)
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