题解 | #Day of Week#

#include <cstdio>
using namespace std;

bool IsLeapYear(int year)
{
    return (year%4==0&&year%100!=0)||(year%400==0);
}

int daytab[2][13]={
    {0,31,28,31,30,31,30,31,31,30,31,30,31},
    {0,31,29,31,30,31,30,31,31,30,31,30,31}
};

string months[13]={" ","January","February","March","April","May",
                   "June","July","August","September","October","November","December"};

string week[8]={"","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};

int calDays(int min_year,int year,int month,int day)
{
    int all_days=0;
    for(int i=min_year;i<year;i++)
    {
        if(IsLeapYear(i)){
            all_days+=366;
        }
        else all_days+=365;
    }
    

    if(IsLeapYear(year)){
       for(int j=1;j<month;j++)
       {
            all_days+=daytab[1][j];
        }
    }
    else{
        for(int j=1;j<month;j++)
        {
            all_days+=daytab[0][j];
        }
    }    
    all_days+=day;
    return all_days;
}

int main()
{
    int year;
    string month;
    int day;
    //while(scanf("%2d%s%4d",&day,&month,&year))
    while(cin>>day>>month>>year)
    {
        int min_year=1;//第一年第一个月第一天为星期一
        int R_months;
        for(int i=1;i<=12;i++)
        {
            if(months[i]==month)
            {
                R_months=i;
                break;
            }
        }
        
        int all_days=calDays(min_year, year, R_months, day);
        int res=all_days%7;
        if(res!=0)
        {
           cout<<week[res]<<endl; 
        }
        else cout<<week[7]<<endl;
    }
    
    return 0;
}