[Project Euler] Problem 19
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)?
这道题，一开始读题误解了意思，浪费了不少时间。注意要求解的是21世纪里有多少个星期天发生在一个月的第一天。
开始自己没用库类，活生生的写出了下面的代码：
def yearbeginweek(year):
""" Function to calculate the week of the first day in a year"""
yearrange = range(1900, year)
days = 0
for x in yearrange:
if x in leapyears:
days = days + 366
else:
days = days + 365
return 1 + days % 7
week = {1: "Mon", 2: "Tue", 3: "Wen", 4: "Thr", 5: "Fri", 6: "Sat", 7: "Sun"}
years = range(1900, 2001)
leapyears = [x for x in years if (x % 4 == 0 and x % 100 != 0) or (x % 100 == 0 and x % 400 == 0)]
nonleapyears = [x for x in years if not x in leapyears]
leapdays = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30]
nonleapdays = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30]
suncount = 0
for year in range(1901, 2001):
# Calculate the first week day in the year
begin = yearbeginweek(year)
if begin == 7:
suncount += 1
begin = 0
# If it is a leap year
if year in leapyears:
for days in leapdays:
if (begin + days % 7) % 7 == 0:
suncount += 1
begin = (begin + days % 7) % 7
else:
for days in nonleapdays:
if (begin + days % 7) % 7 == 0:
suncount += 1
begin = (begin + days % 7) % 7
print suncount
这个比较囧，后来看了有个Datetime module，一句话就可以解决这个问题了：
import datetime print len([datetime.date(year, month, 1) for year in range(1901, 2001) for month in range(1, 13) if datetime.date(year, month, 1).weekday() == 6])
这不得不佩服python的类库实在强大。