效率非常高的判断某天是星期几的代码

#include

int main( void )
{
    //W= (d+2*m+3*(m+1)/5+y+y/4-y/100+y/400) mod 7
    int w, d, m, y;
    char day[][10]={"Mon", "Tue", "Wen", "Thu", "Fri", "Sat","Sun"};
    scanf("%d%d%d", &y, &m, &d);
    if(m<=2) y--, m+=12;
    w = (d+2*m+3*(m+1)/5+y+y/4-y/100+y/400) % 7;
    printf("%s\n", day[w]);
}