Project Euler 19

题目

Counting Sundays

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 \(2000\))?

解决方案

可以使用Python中datetime包的date类解决。

代码

from datetime import date

l = 1901
r = 2000
ans = 0
for y in range(l, r + 1):
    for m in range(1, 13):
        if date(y, m, 1).isoweekday() == 7:
            ans += 1
print(ans)