Counting Sundays

Description

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 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)?

Solution

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def solution():
    month_day_dict = {
        1: 31,
        2: 28,
        3: 31,
        4: 30,
        5: 31,
        6: 30,
        7: 31,
        8: 31,
        9: 30,
        10: 31,
        11: 30,
        12: 31,
    }

    def is_leap_year(year):
        if year % 4 == 0 and year % 400 == 0:
            return True
        return False

    init = 0
    count = 0
    for i in range(1900, 2001):
        if is_leap_year(i):
            month_day_dict[2] = 29
        for j in range(1, 13):
            for k in range(1, month_day_dict[j]):
                init += 1
                init %= 7
                if init == 0 and k == 1 and i >= 1901:
                    count += 1
                    print(f"The year {i} and month {j} the first day is sunday")
    return count

Summary

简单总结下这道题

对于每个月的天数可以打表,常见的处理方式就是字典
判断年份是否闰年来确定 2月的天数
结果是获取每个月第一天是星期天的月份个数
初始值1900年一月一号是星期一和求值区间是从1901年开始

Contents

Description

Solution

Summary