1185. Day of the Week

Given a date, return the corresponding day of the week for that date.

The input is given as three integers representing the day, month and year respectively.

Return the answer as one of the following values {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}.

 

Example 1:

Input: day = 31, month = 8, year = 2019
Output: "Saturday"
Example 2:

Input: day = 18, month = 7, year = 1999
Output: "Sunday"
Example 3:

Input: day = 15, month = 8, year = 1993
Output: "Sunday"
 

Constraints:

The given dates are valid dates between the years 1971 and 2100.

这题不难，直接计算出相对于1971年1月1日（星期五）的天数，然后对其和7进行取余即可。

class DayOfTheWeek : public Solution {
public:
    void Exec() {

    }
    string dayOfTheWeek(int day, int month, int year) {
        string week_names[] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

        int days = 0;
        for (int i = 1971; i < year; i++) {
            if (i % 4 == 0) {
                if (i % 100 == 0 && i % 400 != 0) {
                    days += 365;
                } else {
                    days += 366;
                }
            } else {
                days += 365;
            }
        }

        for (int i = 1; i < month; i++) {
            if (i == 1 || i == 3 || i == 5 || i == 7 || i == 8 || i == 10 ||
                i == 12) {
                days += 31;
            } else if (i == 2) {
                if (year % 4 == 0) {
                    if (year % 100 == 0 && year % 400 != 0) {
                        days += 28;
                    } else {
                        days += 29;
                    }
                } else {
                    days += 28;
                }
            } else {
                days += 30;
            }
        }

        days += day;
        days %= 7;
        return week_names[(4 + days) % 7];
    }
};