1118 Number of Days in a Month

Given a year year and a month month, return the number of days of that month.

Example 1:

Input: year = 1992, month = 7
Output: 31

Example 2:

Input: year = 2000, month = 2
Output: 29

Example 3:

Input: year = 1900, month = 2
Output: 28

Constraints:

• 1583 <= year <= 2100

• 1 <= month <= 12

一开始还以为很简单，后来百度一下才知道闰年的规则这么复杂。小学时候被骗了。其实是，一般的年，能被4整除，不被100整除就是闰年。如果是百年的话，要被400整除才是闰年。

public int numberOfDays(int year, int month) {
    if (year < 0 || month < 1 || month > 12) {
        return -1;
    }
    
    int[] daysInMonthExceptFeb = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};       
    if (month == 2 && year % 4 == 0) {            
        if (year % 100 == 0) {
            if (year % 400 == 0) {
                return 29;
            } else {}
                return 28;
            }
        } else {
            return 29;    
        }
    } else {
        return daysInMonthExceptFeb[month - 1];
    }
}