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)?

很直接的,查下表1901/1/1是星期二,此时设表示周几的变量numOfDay = 2,那么1901/2/1是周几？只要numOfDay加上一月份的天数31,再模7得5知为周五.依此法检测1901~2000每月第一天是周几。注意:别忘了2月份的天数需要是否闰年的判断.

171

Source:C++