# 1118. Number of Days in a Month

## Description

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

## Solutions

Solution 1: Determine Leap Year

We can first determine whether the given year is a leap year. If the year can be divided by $4$ but not by $100$, or can be divided by $400$, then this year is a leap year.

February has $29$ days in a leap year and $28$ days in a common year.

We can use an array $days$ to store the number of days in each month of the current year, where $days[0]=0$, $days[i]$ represents the number of days in the $i$th month of the current year. Then the answer is $days[month]$.

The time complexity is $O(1)$, and the space complexity is $O(1)$.

• class Solution {
public int numberOfDays(int year, int month) {
boolean leap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
int[] days = new int[] {0, 31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
return days[month];
}
}

• class Solution {
public:
int numberOfDays(int year, int month) {
bool leap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
vector<int> days = {0, 31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
return days[month];
}
};

• class Solution:
def numberOfDays(self, year: int, month: int) -> int:
leap = (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0)
days = [0, 31, 29 if leap else 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
return days[month]


• func numberOfDays(year int, month int) int {
leap := (year%4 == 0 && year%100 != 0) || (year%400 == 0)
x := 28
if leap {
x = 29
}
days := []int{0, 31, x, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
return days[month]
}

• function numberOfDays(year: number, month: number): number {
const leap = (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
const days = [0, 31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
return days[month];
}