HDU 2133 What day is it（给定日期求星期几）

[align=left]Problem Description[/align]
Today is Saturday, 17th Nov,2007. Now, if i tell you a date, can you tell me what day it is ?

[align=left]Input[/align]
There are multiply cases.

One line is one case.

There are three integers, year(0<year<10000), month(0<=month<13), day(0<=day<32).

[align=left]Output[/align]
Output one line.

if the date is illegal, you should output "illegal". Or, you should output what day it is.

[align=left]Sample Input[/align]

2007 11 17

[align=left]Sample Output[/align]

Saturday
思路见AC代码：

#include<stdio.h>
int run(int m)
{
if((m%4==0&&m%100!=0)||(m%400==0))
return 1;
else
return 0;
}
void print(int m)
{
switch(m)
{
case 2:
printf("Monday\n");
break;
case 3:
printf("Tuesday\n");
break;
case 4:
printf("Wednesday\n");
break;
case 5:
printf("Thursday\n");
break;
case 6:
printf("Friday\n");
break;
case 0:
printf("Saturday\n");
break;
case 7:
printf("Saturday\n");
break;
case 1:
printf("Sunday\n");
break;
}
}
int main()
{
int a[]= {0,31,28,31,30,31,30,31,31,30,31,30,31};
int dup,dn;
int y,m,d;
int sd,i;                             //天数总差
int weak,x;
dn=0;
for(i=1; i<11; i++)
dn=dn+a[i];
dn=dn+17;
dup=0;
dup=dup+a[12]+13;
int ffff;
while(scanf("%d%d%d",&y,&m,&d)!=EOF)
{
ffff=0;
if(0<y&&y<10000&&0<m&&m<13&&0<d&&d<32)  //细节很重要，这里WA好几次....
{
if(d<=a[m]||(m==2&&d<=29&&run(y)))
{
ffff=1;
}
}
sd=0;
if(ffff)
{
if(y>2007)
{
x=y-2007-1;
sd=sd+x*365;
for(i=2007; i<y; i++)
{
if(run(i))
sd++;
}
for(i=1; i<m; i++)
sd=sd+a[i];             //加上月
sd=sd+d;                //加上天
if(m>2&&run(y))         //如果本年是闰年且月份大于2
sd++;
sd=sd+dup;
weak=(sd)%7;            //一周7天,因为2007,11,17星期六,所以sd+1
print(weak);
}
else if((y==2007&&m>11)||(y==2007&&m==11&&d>=17))
{
if(m>11)
sd=sd+13+d;
else
sd=sd+d-17;
weak=(sd)%7;            //一周7天,因为2007,11,17星期六,所以sd+1
print(weak);
}
else if(y<2007)
{
x=2007-(y+1);
sd=sd+x*365;
for(i=y+1; i<2007; i++)
{
if(run(i))
sd++;
}
for(i=m+1; i<=12; i++)
sd=sd+a[i];
if(m<=2&&run(y))
sd++;
sd=sd+(a[m]-d);
sd=sd+dn;
weak=7-(sd)%7;            //一周7天,因为2007,11,17星期六,所以sd+1
print(weak);
}
else if((y==2007&&m<11)||(y==2007&&m==11&&d<17))
{
if(m<11)
{
for(i=m+1; i<11; i++)
sd=sd+a[i];
sd=sd+(a[m]-d)+17;
}
else
{
sd=sd+(17-d);
}
weak=7-(sd)%7;            //一周7天,因为2007,11,17星期六,所以sd+1
print(weak);
}
}
else
{
printf("illegal\n");
}
}
return 0;
}

再上一个公式：

int whatday(int y,int m,int d)  //蔡勒公式.注意：只适用1582-10-5之后
{
int ans ;
if(m==1||m==2)
m=m+12,y--;
if((y<1752)||(y==1752&&m<9)||(y==1752&&m==9&&d<3))
ans=(d+2*m+3*(m+1)/5+y+y/4+5)%7;             //1752-9-3之前
else
ans=(d+2*m+3*(m+1)/5+y+y/4-y/100+y/400)%7;   //1752-9-3之后（包括9-3）
return ans;                                  //返回值+1就是对应星期几
}