计算星期几

版权声明：小简原创 https://blog.csdn.net/qq_43469554/article/details/87625994

已知1年1月1号是星期一
①暴力求解：

#include<iostream>
#include<string>
using namespace std;
string weekday[7] = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
int monthday[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int is_leap(int y)
{
	return y % 4 == 0 && y % 100 != 0 || y % 400 == 0;
}
int whatday(int y, int m, int d) 
{
	int ans = 0;
    for (int i = 1; i < y; i++)
    {
    	if(is_leap(i))
    	{
    		ans += 366 % 7;
    		ans %= 7;
		}
		else
		{
			ans += 365 % 7;
			ans %= 7;
		}
	}
	for (int i = 1; i < m; i++)
	{
		ans += monthday[i] % 7 + (is_leap(y) && i == 2);
		ans %= 7;
	}
	ans += (d - 1) % 7;
	ans %= 7;
	return ans;
}
int main() 
{
    int y, m, d;
    cin >> y >> m >> d;
    cout << weekday[whatday(y, m, d)] << endl;
    return 0;
}

②利用吉姆拉尔森公式：

#include<iostream>
#include<string>
using namespace std;
int whatday(int y, int m, int d) 
{
    if (m <= 2)
    {
        m += 12;
        y--;
    }
    return (d + m * 2 + 3 * (m + 1) / 5 + y + y / 4 - y / 100 + y / 400) % 7;
}
string weekday[7] = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
int main() 
{
    int y, m, d;
    cin >> y >> m >> d;
    cout << weekday[whatday(y, m, d)] << endl;
    return 0;
}