44 lines
1.2 KiB
Ruby
44 lines
1.2 KiB
Ruby
descr=%{
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You are given the following information,
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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,
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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
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twentieth century (1 Jan 1901 to 31 Dec 2000)?
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}
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nbdaysbymonth=[31,28,31,30,31,30,31,31,30,31,30,31]
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# 0 Monday, ... , 6 Sunday
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day_of_month=0
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nb_sunday=0
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(1900..2000).each do |year|
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is_leap = ( year % 4 == 0 )
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if ( year % 100 == 0 ) && ( year % 400 != 0 )
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is_leap = false
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end
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if is_leap
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nbdaysbymonth[1]=29
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else
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nbdaysbymonth[1]=28
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end
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(0..11).each do |month|
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# puts "1st #{month+1}/#{year} = #{day_of_month}"
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if day_of_month == 6 && year >= 1901
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puts "* #{month+1}/#{year}"
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nb_sunday += 1
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end
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day_of_month = ( day_of_month + nbdaysbymonth[month] ) % 7
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end
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end
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puts nb_sunday
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