nyoj-219-An problem about date

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<math.h>
using namespace std;
int main()
{
    int year,month,day,c,y,week;
    while(scanf("%d%d%d",&year,&month,&day)!=EOF)
    {
        if(month==1||month==2)//判断month是否为1或2
        {
        year--;
        month+=12;
        }
        c=year/100;
        y=year-c*100;
        week=y+(y/4)+(c/4)-2*c+(26*(month+1)/10)+day-1;
        printf("%d\n",(week%7+7)%7);
    }
    return 0;
}

这个题就是公式   前提是 你得知道并且会用