How to check if the given string is palindrome? [closed]

Question

PHP sample:

$string = "A man, a plan, a canal, Panama";

function is_palindrome($string)
{
    $a = strtolower(preg_replace("/[^A-Za-z0-9]/","",$string));
    return $a==strrev($a);
}

Removes any non-alphanumeric characters (spaces, commas, exclamation points, etc.) to allow for full sentences as above, as well as simple words.

Windows XP (might also work on 2000) or later BATCH script:

@echo off

call :is_palindrome %1
if %ERRORLEVEL% == 0 (
    echo %1 is a palindrome
) else (
    echo %1 is NOT a palindrome
)
exit /B 0

:is_palindrome
    set word=%~1
    set reverse=
    call :reverse_chars "%word%"
    set return=1
    if "$%word%" == "$%reverse%" (
        set return=0
    )
exit /B %return%

:reverse_chars
    set chars=%~1
    set reverse=%chars:~0,1%%reverse%
    set chars=%chars:~1%
    if "$%chars%" == "$" (
        exit /B 0
    ) else (
        call :reverse_chars "%chars%"
    )
exit /B 0

Language agnostic meta-code then...

rev = StringReverse(originalString)
return ( rev == originalString );

C# in-place algorithm. Any preprocessing, like case insensitivity or stripping of whitespace and punctuation should be done before passing to this function.

boolean IsPalindrome(string s) {
    for (int i = 0; i < s.Length / 2; i++)
    {
        if (s[i] != s[s.Length - 1 - i]) return false;
    }
    return true;
}

---

Edit: removed unnecessary "+1" in loop condition and spent the saved comparison on removing the redundant Length comparison. Thanks to the commenters!

C#: LINQ

var str = "a b a";
var test = Enumerable.SequenceEqual(str.ToCharArray(), 
           str.ToCharArray().Reverse());

A more Ruby-style rewrite of Hal's Ruby version:

class String
  def palindrome?
    (test = gsub(/[^A-Za-z]/, '').downcase) == test.reverse
  end
end

Now you can call palindrome? on any string.

Unoptimized Python:

>>> def is_palindrome(s):
...     return s == s[::-1]