using NUnit.Framework;

​

public class PalindromeChecker

{

    /// <summary>

    /// Checks if a given input string or number is a palindrome.

    /// </summary>

    /// <param name="input">The input string or number to check.</param>

    /// <returns>A string indicating whether the input is a palindrome and its type (string or number). Returns an error message if the input is invalid.</returns>

    public string IsPalindrome(string input)

    {

        // Input validation: Check for null or empty input

        if (string.IsNullOrEmpty(input))

        {

            return "Error: Input cannot be null or empty.";

        }

​

        // Input validation: Check for whitespace-only input

        if (string.IsNullOrWhiteSpace(input))

        {

            return "Error: Input cannot be whitespace only.";

        }

​

        // Check if the input is a number

        if (IsNumeric(input))

        {

            // Optimized palindrome check for numbers

            if (IsPalindromeNumber(input))

            {

                return $"{input} is a Palindrome number.";

            }

            else

            {

                return $"{input} is not a Palindrome number.";

            }

        }

        else

        {

            // Optimized palindrome check for strings (case-insensitive)

            if (IsPalindromeString(input))

            {

                return $"{input} is a Palindrome string.";

            }

            else

            {

                return $"{input} is not a Palindrome string.";

            }

        }

    }

​

    /// <summary>

    /// Helper function to determine if a string is numeric.

    /// </summary>

    /// <param name="str">The string to check.</param>

    /// <returns>True if the string is numeric, False otherwise.</returns>

    private bool IsNumeric(string str)

    {

        return int.TryParse(str, out _); // Use int.TryParse for efficiency

    }

​

    /// <summary>

    /// Optimized helper function to check if a number string is a palindrome.

    /// </summary>

    /// <param name="numberStr">The number string to check.</param>

    /// <returns>True if the number is a palindrome, False otherwise.</returns>

    private bool IsPalindromeNumber(string numberStr)

    {

        int left = 0;

        int right = numberStr.Length - 1;

​

        while (left < right)

        {

            if (numberStr[left] != numberStr[right])

            {

                return false;

            }

            left++;

            right--;

        }

​

        return true;

    }

​

​

    /// <summary>

    /// Optimized helper function to check if a string is a palindrome (case-insensitive).

    /// </summary>

    /// <param name="str">The string to check.</param>

    /// <returns>True if the string is a palindrome, False otherwise.</returns>

    private bool IsPalindromeString(string str)

    {

        string cleanStr = str.ToLower(); // Convert to lowercase for case-insensitive comparison

        int left = 0;

        int right = cleanStr.Length - 1;

​

        while (left < right)

        {

            if (cleanStr[left] != cleanStr[right])

            {

                return false;

            }

            left++;

            right--;

        }

​

        return true;

    }

}

​

[TestFixture]

public class PalindromeCheckerTests

{

    private PalindromeChecker palindromeChecker;

​

    [SetUp]

    public void Setup()

    {

        palindromeChecker = new PalindromeChecker();

    }

​

    [Test]

    public void IsPalindrome_ValidPalindromeString_ReturnsTrue()

    {

        Assert.That(palindromeChecker.IsPalindrome("madam"), Is.EqualTo("madam is a Palindrome string."));

        Assert.That(palindromeChecker.IsPalindrome("Aba"), Is.EqualTo("Aba is a Palindrome string."));

        Assert.That(palindromeChecker.IsPalindrome("level"), Is.EqualTo("level is a Palindrome string."));

    }

​

    [Test]

    public void IsPalindrome_ValidNonPalindromeString_ReturnsFalse()

    {

        Assert.That(palindromeChecker.IsPalindrome("Welcome"), Is.EqualTo("Welcome is not a Palindrome string."));

        Assert.That(palindromeChecker.IsPalindrome("hello"), Is.EqualTo("hello is not a Palindrome string."));

    }

​

    [Test]

    public void IsPalindrome_ValidPalindromeNumber_ReturnsTrue()

    {

        Assert.That(palindromeChecker.IsPalindrome("121"), Is.EqualTo("121 is a Palindrome number."));

        Assert.That(palindromeChecker.IsPalindrome("12321"), Is.EqualTo("12321 is a Palindrome number."));

    }

​

    [Test]

    public void IsPalindrome_ValidNonPalindromeNumber_ReturnsFalse()

    {

        Assert.That(palindromeChecker.IsPalindrome("123"), Is.EqualTo("123 is not a Palindrome number."));

        Assert.That(palindromeChecker.IsPalindrome("12345"), Is.EqualTo("12345 is not a Palindrome number."));

    }

​

    [Test]

    public void IsPalindrome_EmptyString_ReturnsError()

    {

        Assert.That(palindromeChecker.IsPalindrome(""), Is.EqualTo("Error: Input cannot be null or empty."));

    }

​

    [Test]

    public void IsPalindrome_NullString_ReturnsError()

    {

        Assert.That(palindromeChecker.IsPalindrome(null), Is.EqualTo("Error: Input cannot be null or empty."));

    }

​

    [Test]

    public void IsPalindrome_WhitespaceString_ReturnsError()

    {

        Assert.That(palindromeChecker.IsPalindrome("   "), Is.EqualTo("Error: Input cannot be whitespace only."));

    }

​

    [Test]

    public void IsPalindrome_MixedCasePalindrome_ReturnsTrue()

    {

        Assert.That(palindromeChecker.IsPalindrome("Racecar"), Is.EqualTo("Racecar is a Palindrome string."));

        Assert.That(palindromeChecker.IsPalindrome("Madam"), Is.EqualTo("Madam is a Palindrome string."));

    }

​

    [Test]

    public void IsPalindrome_StringWithSpaces_ReturnsFalse()

    {

        Assert.That(palindromeChecker.IsPalindrome("A man a plan a canal Panama"), Is.EqualTo("A man a plan a canal Panama is not a Palindrome string."));

    }

​

    [Test]

    public void IsPalindrome_NegativeNumber_ReturnsFalse()

    {

        Assert.That(palindromeChecker.IsPalindrome("-121"), Is.EqualTo("-121 is not a Palindrome number."));

    }

​

    [Test]

    public void IsPalindrome_SingleCharacter_ReturnsTrue()

    {

        Assert.That(palindromeChecker.IsPalindrome("a"), Is.EqualTo("a is a Palindrome string."));

        Assert.That(palindromeChecker.IsPalindrome("1"), Is.EqualTo("1 is a Palindrome number."));

    }

}

​

public class Program

{

    public static void Main()

    {

        new NUnitLite.AutoRun().Execute(["--noc" /*no colored output for .Net Fiddle*/]);

    }

}