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.

Solution:

class Solution {
    public String dayOfTheWeek(int day, int month, int year) {
        String[] week = new String[]{"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
        int[] days = new int[]{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

        if (isLeapYear(year)){
            days[1] = 29;
        }

        int count = 0;
        // Calculate total days from 1971 to the previous year
        for (int i = 1971; i < year; i++){
            if (i % 4 == 0){
                count = count + 366;

            }else{
                count = count + 365;
            }
        }

        // Add days from the beginning of the current year to the previous month
        for (int i = 0; i < month - 1; i++){
            count = days[i] + count;
        }

        // Add the days in the current month
        count = count + day;

        // // January 1, 1971, was a Friday, which is the 5th day in the week array
        return week[(count + 4) % 7];
    }

    private boolean isLeapYear(int year){
        return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
    }
}