Leap Year

Problem link : Leap Year

Problem: Check if a Year is a Leap Year

Problem Statement

You are given an integer n representing a year. Your task is to determine whether the year is a leap year or not.

Definition of a Leap Year:

A year is a leap year if:

It is divisible by 4, and
It is not divisible by 100, unless it is also divisible by 400

Examples

Example 1:
Input: n = 4
Output: true
Explanation: 4 is divisible by 4 and not divisible by 100, so it's a leap year.

Example 2:
Input: n = 2021
Output: false
Explanation: 2021 is not divisible by 4, so it's not a leap year.

Intuition

To check whether a given year is a leap year, follow the leap year rules. These are well-known rules used in the Gregorian calendar.

If a year is divisible by 400, it is a leap year.
If a year is divisible by 100 but not by 400, it is not a leap year.
If a year is divisible by 4 but not by 100, it is a leap year.
Otherwise, it is not a leap year.

Approach

Use a simple conditional check using the above rules:

(N % 4 == 0 && N % 100 != 0) || (N % 400 == 0)

This condition directly implements the leap year logic.

Code (Java)

// User function Template for Java
class Solution {
    static boolean isLeap(int N) {
        return (N % 4 == 0 && N % 100 != 0) || (N % 400 == 0);
    }
}

Time and Space Complexity

Time Complexity: O(1)
Only constant-time arithmetic and logical operations are performed.
Space Complexity: O(1)
No additional memory is used.

Dry Run

Input: `N = 2000`

2000%4=0 ✅
2000%100=0 ✅
2000%400=0 ✅
So: (true && false) || true = true

Output: true

Input: `N = 1900`

1900%4=0 ✅
1900%100=0✅
1900%400=300 ❌
So: (true && false) || false = false

Output: false

Input: `N = 2024`

2024%4=0 ✅
2024%100=24 ❌
So: true && true = true