蔡勒公式

#include<iostream>

using namespace std;

//蔡勒公式  給定年月日 算出此天是星期幾
int weekday(int year,int month,int day) {
	if(month == 1 || month == 2){
		month += 12;
		year--;
	}
	int c = year / 100;
	int y = year % 100;
	int m = month;
	int d = day;
	int w = c / 4 - 2 *c + y + y / 4 + 26*(m+1) / 10 + d - 1;
	if
 
(w < 0)
		return (w + (-w / 7 + 1) * 7) % 7;
	return w % 7;
}

int main(){
	cout<<weekday(2020,2,1)<<endl;
	return 0; 
}