Question
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)?
Analysis
- 闰年影响到二月的天数，闰年的判断可以用函数实现。
- 星期天的判断方法就是所要求的日期距1900.1.1的天数对7取余。
Program
def isLeapYear(year):
if (year % 400 == 0):
return True
elif (year % 100 == 0):
return False
elif (year % 4 == 0):
return True
else:
return False
def isSunday(day):
if (day % 7 == 6):
return True
else:
return False
days = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
num_sundays = 0
index = sum(days)
if (isLeapYear(1900)):
index += 1
for year in range(1901, 2001):
if (isLeapYear(year)):
days[1] = 29
else:
days[1] = 28
for mouth in range(12):
if (isSunday(index)):
num_sundays += 1
index += days[mouth]
print(num_sundays)
