PHP Program to Check Palindrome String

Use strrev() to reverse the string and compare it with the original using if ($string === strrev($string)) to check if it is a palindrome.

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, think about reading it forwards and backwards. If both are exactly the same, then the string is a palindrome. So, reverse the string and compare it with the original string to decide.

Algorithm

1

Get the input string.

2

Reverse the input string.

3

Compare the original string with the reversed string.

4

If both are equal, return that it is a palindrome.

5

Otherwise, return that it is not a palindrome.

Code

php

<?php
$string = "madam";
if ($string === strrev($string)) {
    echo "$string is a palindrome";
} else {
    echo "$string is not a palindrome";
}
?>

Output

madam is a palindrome

Dry Run

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

1

Input string

$string = "madam"

2

Reverse string

strrev($string) = "madam"

3

Compare strings

"madam" === "madam" is true

4

Output result

Print 'madam is a palindrome'

Original String	Reversed String	Comparison Result
madam	madam	true

Why This Works

Step 1: Reverse the string

The strrev() function creates a reversed copy of the input string.

Step 2: Compare original and reversed

Using === checks if both strings are exactly the same, including case.

Step 3: Print result

If they match, the string is a palindrome; otherwise, it is not.

Alternative Approaches

Manual character comparison

php

<?php
$string = "madam";
$len = strlen($string);
$isPalindrome = true;
for ($i = 0; $i < $len / 2; $i++) {
    if ($string[$i] !== $string[$len - $i - 1]) {
        $isPalindrome = false;
        break;
    }
}
if ($isPalindrome) {
    echo "$string is a palindrome";
} else {
    echo "$string is not a palindrome";
}
?>

This method checks characters one by one without creating a reversed string, saving memory for very long strings.

Using strtolower for case insensitive check

php

<?php
$string = "Madam";
$lower = strtolower($string);
if ($lower === strrev($lower)) {
    echo "$string is a palindrome";
} else {
    echo "$string is not a palindrome";
}
?>

This approach ignores case differences by converting the string to lowercase before checking.

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

Time Complexity

The program reverses the string which takes O(n) time where n is the string length, and then compares two strings in O(n) time, so overall O(n).

Space Complexity

The reversed string requires O(n) extra space. The manual comparison alternative uses O(1) space.

Which Approach is Fastest?

Using strrev() is simple and fast for most cases, but manual character comparison saves memory for very large strings.

Approach	Time	Space	Best For
Using strrev()	O(n)	O(n)	Simple and quick palindrome check
Manual character comparison	O(n)	O(1)	Memory efficient for large strings
Case insensitive check with strtolower	O(n)	O(n)	Ignoring letter case in palindrome check