// This is a solution to a question that was asked as part of:

// https://www.devleader.ca/2023/09/02/tons-of-beginner-resources-dev-leader-weekly-7/

​

using System;

​

bool IsPalindrome(string input)

{

    if (string.IsNullOrWhiteSpace(input))

    {

        return false;

    }

​

    // Create a Span from the input string

    var inputSpan = input.AsSpan();

    // Pointers to the start and end of the span

    int left = 0, right = inputSpan.Length - 1;

​

    while (left < right)

    {

        // Skip non-alphanumeric characters from the left

        while (left < right && !char.IsLetterOrDigit(inputSpan[left]))

            left++;

​

        // Skip non-alphanumeric characters from the right

        while (left < right && !char.IsLetterOrDigit(inputSpan[right]))

            right--;

​

        // If characters do not match (case insensitive), then it's not a palindrome

        if (char.ToLowerInvariant(inputSpan[left]) != char.ToLowerInvariant(inputSpan[right]))

            return false;

​

        left++;

        right--;

    }

​

    return true;

}

​

void Test(string input)

{

    Console.WriteLine($"{input}: {IsPalindrome(input)}");

}

​

Test("hello world");

Test(null);

Test("");

Test("    ");

Test("race car");

Test("racecar");

Test("RaCeCaR");

Test("1");

Test("11");

Test("111");