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)