How to check if String is Palindrome using C#?

A palindrome is a string that reads the same forwards and backwards, such as "Level", "madam", or "racecar". In C#, there are several ways to check if a string is a palindrome.

Using Array.Reverse() Method

The simplest approach is to reverse the string and compare it with the original. First, convert the string to a character array −

char[] ch = str.ToCharArray();

Then reverse the array using Array.Reverse() −

Array.Reverse(ch);

Finally, compare the reversed string with the original using case-insensitive comparison −

bool res = str.Equals(rev, StringComparison.OrdinalIgnoreCase);

Example

using System;

class Program {
   static void Main(string[] args) {
      string str, rev;
      str = "Level";
      char[] ch = str.ToCharArray();
      Array.Reverse(ch);
      rev = new string(ch);
      bool res = str.Equals(rev, StringComparison.OrdinalIgnoreCase);
      
      if (res == true) {
         Console.WriteLine("String " + str + " is a Palindrome!");
      } else {
         Console.WriteLine("String " + str + " is not a Palindrome!");
      }
   }
}

The output of the above code is −

String Level is a Palindrome!

Using Two-Pointer Technique

A more efficient approach uses two pointers to compare characters from both ends moving towards the center −

using System;

class Program {
   static bool IsPalindrome(string str) {
      int left = 0;
      int right = str.Length - 1;
      
      while (left < right) {
         if (char.ToLower(str[left]) != char.ToLower(str[right])) {
            return false;
         }
         left++;
         right--;
      }
      return true;
   }
   
   static void Main(string[] args) {
      string[] testStrings = {"Level", "hello", "racecar", "A man a plan a canal Panama"};
      
      foreach (string str in testStrings) {
         string cleanStr = str.Replace(" ", "");
         if (IsPalindrome(cleanStr)) {
            Console.WriteLine("'" + str + "' is a Palindrome!");
         } else {
            Console.WriteLine("'" + str + "' is not a Palindrome!");
         }
      }
   }
}

The output of the above code is −

'Level' is a Palindrome!
'hello' is not a Palindrome!
'racecar' is a Palindrome!
'A man a plan a canal Panama' is a Palindrome!

Using LINQ Reverse()

You can also use LINQ to reverse the string and compare −

using System;
using System.Linq;

class Program {
   static void Main(string[] args) {
      string str = "madam";
      string reversed = new string(str.Reverse().ToArray());
      
      bool isPalindrome = string.Equals(str, reversed, StringComparison.OrdinalIgnoreCase);
      
      if (isPalindrome) {
         Console.WriteLine("'" + str + "' is a Palindrome!");
      } else {
         Console.WriteLine("'" + str + "' is not a Palindrome!");
      }
   }
}

The output of the above code is −

'madam' is a Palindrome!

Performance Comparison

Conclusion

Checking for palindromes in C# can be accomplished using various methods. The two-pointer technique is most efficient for memory usage, while Array.Reverse() offers simplicity. Choose the method that best fits your performance requirements and coding style preferences.