PowerShell Script to Check Palindrome String

Use $input -eq -join ($input.ToCharArray()[-1..-($input.Length)]) in PowerShell to check if a string is a palindrome by comparing it to its reversed version.

Examples

Inputmadam

Outputmadam is a palindrome.

Inputhello

Outputhello is not a palindrome.

InputA

OutputA is a palindrome.

How to Think About It

To check if a string is a palindrome, compare the original string with its reversed version. If both are the same, the string reads the same forwards and backwards, so it is a palindrome.

Algorithm

1

Get the input string.

2

Convert the string into an array of characters.

3

Reverse the array of characters.

4

Join the reversed characters back into a string.

5

Compare the original string with the reversed string.

6

Return whether the string is a palindrome based on the comparison.

Code

powershell

function Test-Palindrome {
    param([string]$input)
    $reversed = -join ($input.ToCharArray()[-1..-($input.Length)])
    if ($input -eq $reversed) {
        Write-Output "$input is a palindrome."
    } else {
        Write-Output "$input is not a palindrome."
    }
}

Test-Palindrome -input "madam"
Test-Palindrome -input "hello"
Test-Palindrome -input "A"

Output

madam is a palindrome.
hello is not a palindrome.
A is a palindrome.

Dry Run

Let's trace the input 'madam' through the code

1

Input string

input = 'madam'

2

Reverse string

reversed = 'madam'

3

Compare original and reversed

'madam' -eq 'madam' is True

Step	Original String	Reversed String	Is Palindrome?
1	madam	madam	True

Why This Works

Step 1: Convert string to array

The string is split into characters using ToCharArray() to allow reversing.

Step 2: Reverse the array

Using array slicing [-1..-length] reverses the character order.

Step 3: Compare strings

The original string is compared to the reversed string with -eq to check palindrome.

Alternative Approaches

Using [string]::Join and Array Reverse

powershell

function Test-PalindromeAlt {
    param([string]$input)
    $chars = $input.ToCharArray()
    [array]::Reverse($chars)
    $reversed = [string]::Join('', $chars)
    if ($input -eq $reversed) {
        Write-Output "$input is a palindrome."
    } else {
        Write-Output "$input is not a palindrome."
    }
}

Test-PalindromeAlt -input "madam"

This method explicitly reverses the array using .NET method, which may be clearer but slightly longer.

Using a loop to build reversed string

powershell

function Test-PalindromeLoop {
    param([string]$input)
    $reversed = ''
    for ($i = $input.Length - 1; $i -ge 0; $i--) {
        $reversed += $input[$i]
    }
    if ($input -eq $reversed) {
        Write-Output "$input is a palindrome."
    } else {
        Write-Output "$input is not a palindrome."
    }
}

Test-PalindromeLoop -input "madam"

This approach uses a manual loop to reverse the string, which is more verbose but easy to understand.

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

Time Complexity

The script processes each character once to reverse the string, so time grows linearly with string length.

Space Complexity

A new array for reversed characters is created, so space also grows linearly with input size.

Which Approach is Fastest?

Using array slicing is concise and efficient; manual loops are slower but clearer for beginners.

Approach	Time	Space	Best For
Array slicing with -join	O(n)	O(n)	Concise and fast for typical use
[array]::Reverse method	O(n)	O(n)	Clear .NET method usage
Manual loop reversal	O(n)	O(n)	Educational clarity, less concise