LINQ :Check whether a string is palindrome or not?

Question

I want to check whether a string is palindrome or not using Linq.

Updated:

I d'nt want to use Reverse function.

Answer 1

var result = Enumerable
                .SequenceEqual(text.ToCharArray(), text.ToCharArray()
                .Reverse());

Answer 2

Using this to reverse the string

new string(Enumerable.Range(1, input.Length).Select(i => input[input.Length - i]).ToArray())

taken from this question you could do something like

public bool isStringPalindrome(String input){
    var reversed = new string(Enumerable.Range(1, input.Length).Select(i => input[input.Length - i]).ToArray());
    return String.Compare(input, reversed, true) == 0;
}

Note this won't take in to consideration punctuation and spacing issues.

Answer 3

It occurs to me that there's an alternate LINQ solution that doesn't require reversing the string.

bool IsPalindrome(string input)
{
    return
        Enumerable.Range(0, input.Length/2)
                    .Select(i => input[i] == input[input.Length - i - 1])
                    .All(b => b);
}

As with the other solutions presented, this assumes an exact palindromic match. It doesn't ignore spaces, punctuation, casing, etc.

It's interesting to note that this solution uses LINQ to implement the same algorithm I showed below in my original answer.

---

Original answer:

I don't know why you'd want to use LINQ for this. Doing it in code is going to be much more efficient and, in my opinion, quite a bit more readable if you just create a method for it.

You can use the same logic that's used to reverse a string:

public bool IsPalindrome(s)
{
    int i = 0;
    int j = s.Length-1;
    while (i > j)
    {
        if (s[i] != s[j])
            return false;
        ++i;
        --j;
    }
    return true;
}

Answer 4

You could use IEnumerable<T>.SequenceEquals method to check if a string is palindrome:

var textA = "ABBA".ToCharArray();
var textB = textA.Reverse();

bool isPalindrome = textA.SequenceEqual(textB);

Answer 5

var testString = "racecar";
//Remove all spaces with a String.Replace if you don't want them counted
//testString = String.Replace(testString, " ", String.Empty);
//and convert to all-lowercase
//testString = testString.ToLowerInvariant();

var forwardArray = testString.ToCharArray();
var reverseArray = forwardArray.Reverse().ToArray();

var isPalindrome = Enumerable.SequenceEqual(forwardArray, reverseArray);

Now, this executes in 2N steps. You can get it down to half that with a simple change:

var testString = "racecar";
//Remove all spaces with a String.Replace if you don't want them counted
//testString = String.Replace(testString, " ", String.Empty);
//and convert to all-lowercase
//testString = testString.ToLowerInvariant();

//take only half the string (rounded down) each way
var length = testString.Length;
var forwardArray = testString.Take(length/2); 
var reverseArray = testString.Reverse().Take(length/2);

var isPalindrome = Enumerable.SequenceEqual(forwardArray, reverseArray);

Answer 6

In C# we write A simple palindrome check It contains a program to reverse a string and to check whether a Entered string is palindrome or not.

    static void Main(string[] args)  
    {  
        string s,revs="";  
        Console.WriteLine(" Enter string");  
        s = Console.ReadLine();  
        for (int i = s.Length-1; i >=0; i--) //String Reverse  
        {  
            revs += s[i].ToString();  
        }  
        if (revs == s) // Checking whether string is palindrome or not  
        {  
            Console.WriteLine("String is Palindrome \n Entered String Was {0} and reverse string is {1}", s, revs);  
        }  
        else  
        {  
            Console.WriteLine("String is not Palindrome \n Entered String Was {0} and reverse string is {1}", s, revs);  
        }  
        Console.ReadKey();  
    }  

Answer 7

A program which takes input as string and check if it is palindrome or not.

import java.util.Scanner;

public class Palindrome {
 public static void main(String args[]) {
    String a, b = "";
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter the string you want to check : ");
    a = sc.nextLine();
    sc.close();
    System.out.println(" ");

    int n = a.length();
    for (int i = n - 1; i >= 0; i--) {
        b = b + a.charAt(i);
    }

    if (a.equalsIgnoreCase(b)) {
        System.out.println("The input string of ''" + a + "'' is 
 palindrome.");
    } else {
        System.out.println("The input string of ''" + a + "'' is not 
  palindrome.");
    }
  }

}