Question

How to check if a string is a palindrome ignoring case and non-alphanumeric characters in C#

Answer 1

using System;
using System.Text; // StringBuilder
using System.Linq;

class PalindromeChecker
{
    static bool IsPalindrome(string str) {
        StringBuilder filtered = new StringBuilder();

        // Filter out non-alphanumeric characters and convert to lowercase
        foreach (char ch in str) {
            if (char.IsLetterOrDigit(ch)) {
                filtered.Append(char.ToLower(ch));
            }
        }

        string clean = filtered.ToString();
        Console.WriteLine(clean);

        // Reverse the filtered string and compare
        string reversed = new string(clean.Reverse().ToArray());
        return clean == reversed;
    }

    static void Main()
    {
        string input = "+^-Ab#c!D 50...#  05*()dcB[]A##@!$";

        if (IsPalindrome(input)) {
            Console.WriteLine("The string is a palindrome.");
        }
        else {
            Console.WriteLine("The string is not a palindrome.");
        }
    }
}



/*
run:
  
abcd5005dcba
The string is a palindrome.
  
*/

 

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Answer 2

using System;
using System.Linq;
using System.Text.RegularExpressions;

class PalindromeChecker
{
    public static bool IsPalindrome(string s) {
        // Remove non-alphanumeric characters and convert to lowercase
        string normalized = Regex.Replace(s, "[^a-zA-Z0-9]", "").ToLower();
        Console.WriteLine(normalized);

        // Reverse the string and compare
        string reversed = new string(normalized.Reverse().ToArray());
        
        return normalized == reversed;
    }

    static void Main()
    {
        string s = "+^-Ab#c!D 50...#  05*()dcB[]A##@!$";
        
        Console.WriteLine(IsPalindrome(s));
    }
}



/*
run:
  
abcd5005dcba
True

*/

 

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