【简单】1185. 一周中的第几天

【题目】
给你一个日期，请你设计一个算法来判断它是对应一周中的哪一天。输入为三个整数：day、month 和 year，分别表示日、月、年。您返回的结果必须是这几个值中的一个 {“Sunday”, “Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”, “Saturday”}
来源：leetcode
链接：https://leetcode-cn.com/problems/day-of-the-week/
【示例】
输入：day = 31, month = 8, year = 2019
输出：“Saturday”
【示例2】
输入：day = 18, month = 7, year = 1999
输出：“Sunday”
【示例3】
输入：day = 15, month = 8, year = 1993
输出：“Sunday”
【提示】
给出的日期一定是在 1971 到 2100 年之间的有效日期
【代码】

class Solution {
public:
//1971-1-1 Friday
//平年365 闰年366    
    bool judge(int year){
        if((year%100!=0&&year%4==0)||(year%400==0))
            return true;
        return false;
    }
    string d[7]={"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
    int tian[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 dayOfTheWeek(int day, int month, int year) {
        day+=4;
        for(int i=1971;i<year;i++)
            if(judge(i))
                day+=366;
            else
                day+=365;
        int flag=judge(year);
        for(int i=1;i<month;i++)
            day+=tian[flag][i];
        return d[day%7];
    }
};

【公式法：基姆拉尔森公式】

class Solution {
public:
    string dayOfTheWeek(int day, int month, int year) {
        if(month==1||month==2) month+=12,year--;
 int iWeek = (day+2*month+3*(month+1)/5+year+year/4-year/100+year/400)%7;                              //基姆拉尔森计算公式
       string result[]= { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday","Sunday"};
 return result[iWeek];
    }
};