PowerShell Script to Check Leap Year

Use the PowerShell code if (($year % 4 -eq 0) -and (($year % 100 -ne 0) -or ($year % 400 -eq 0))) { 'Leap Year' } else { 'Not Leap Year' } to check if a year is a leap year.

Examples

Input2000

OutputLeap Year

Input1900

OutputNot Leap Year

Input2024

OutputLeap Year

How to Think About It

To check if a year is leap, first see if it divides evenly by 4. If yes, then check if it is not divisible by 100 unless it is also divisible by 400. This ensures correct leap year rules.

Algorithm

1

Get the input year.

2

Check if the year is divisible by 4.

3

If divisible by 4, check if it is not divisible by 100 or divisible by 400.

4

If conditions hold, return 'Leap Year', else return 'Not Leap Year'.

Code

powershell

param([int]$year)
if (($year % 4 -eq 0) -and (($year % 100 -ne 0) -or ($year % 400 -eq 0))) {
    Write-Output 'Leap Year'
} else {
    Write-Output 'Not Leap Year'
}

Output

Leap Year

Dry Run

Let's trace the year 1900 through the code

1

Check divisibility by 4

1900 % 4 = 0 (true)

2

Check divisibility by 100

1900 % 100 = 0 (true)

3

Check divisibility by 400

1900 % 400 = 300 (false)

4

Final decision

Since divisible by 100 but not by 400, result is 'Not Leap Year'

Year	Divisible by 4	Divisible by 100	Divisible by 400	Leap Year?
1900	Yes	Yes	No	No

Why This Works

Step 1: Divisible by 4

A leap year must be divisible by 4, so we check year % 4 -eq 0.

Step 2: Not divisible by 100 unless divisible by 400

Years divisible by 100 are not leap years unless also divisible by 400, checked by ($year % 100 -ne 0) -or ($year % 400 -eq 0).

Alternative Approaches

Using DateTime TryParseExact

powershell

param([int]$year)
try {
    $date = [datetime]::ParseExact("29/02/$year", 'dd/MM/yyyy', $null)
    Write-Output 'Leap Year'
} catch {
    Write-Output 'Not Leap Year'
}

This method tries to create Feb 29 date; if it fails, year is not leap. It is less efficient but uses built-in date parsing.

Using switch statement

powershell

param([int]$year)
switch ($true) {
    ($year % 400 -eq 0) { Write-Output 'Leap Year'; break }
    ($year % 100 -eq 0) { Write-Output 'Not Leap Year'; break }
    ($year % 4 -eq 0) { Write-Output 'Leap Year'; break }
    default { Write-Output 'Not Leap Year' }
}

This approach uses switch for clearer logic flow but is longer.

Complexity: O(1) time, O(1) space

Time Complexity

The script performs a fixed number of arithmetic operations and comparisons, so it runs in constant time.

Space Complexity

Only a few variables are used, so space usage is constant.

Which Approach is Fastest?

The modulo arithmetic method is fastest and simplest; using DateTime parsing is slower but leverages built-in validation.

Approach	Time	Space	Best For
Modulo Arithmetic	O(1)	O(1)	Simple and fast leap year check
DateTime Parsing	O(1)	O(1)	Using built-in date validation, less efficient
Switch Statement	O(1)	O(1)	Clear logic flow, slightly longer code