C# Online Compiler | .NET Fiddle

using System;

public class Program
{
	public static string GetInnermostString(string input, string startDelimiter, string endDelimiter)
	{
		if (string.IsNullOrEmpty(input) || string.IsNullOrEmpty(startDelimiter) || string.IsNullOrEmpty(endDelimiter))
			return null;

		int innermostStart = -1;
		int innermostEnd = -1;
		int nestingLevel = 0;
		int maxNestingLevel = 0;

		for (int i = 0; i < input.Length - startDelimiter.Length + 1; i++)
		{
			if (input.Substring(i, startDelimiter.Length) == startDelimiter)
			{
				nestingLevel++;
				if (nestingLevel > maxNestingLevel)
				{
					maxNestingLevel = nestingLevel;
					innermostStart = i;
				}
				i += startDelimiter.Length - 1;
			}
			else if (i <= input.Length - endDelimiter.Length && 
					 input.Substring(i, endDelimiter.Length) == endDelimiter)
			{
				nestingLevel--;
				i += endDelimiter.Length - 1;
			}
		}

		if (innermostStart == -1 || nestingLevel != 0)
			return null;

		nestingLevel = 0;
		for (int i = innermostStart; i < input.Length - endDelimiter.Length + 1; i++)
		{
			if (input.Substring(i, startDelimiter.Length) == startDelimiter)
			{
				nestingLevel++;
				i += startDelimiter.Length - 1;
			}
			else if (input.Substring(i, endDelimiter.Length) == endDelimiter)
			{
				nestingLevel--;
				if (nestingLevel == 0)
				{
					innermostEnd = i + endDelimiter.Length;
					break;
				}
				i += endDelimiter.Length - 1;
			}
		}

		if (innermostEnd == -1)
			return null;

		return input.Substring(innermostStart + startDelimiter.Length, 
							   innermostEnd - innermostStart - startDelimiter.Length - endDelimiter.Length);
	}

	// Example usage
	public static void Main()
	{   
        Console.WriteLine("Grok AI Generated Code for GetInnermostString function"); 
		//string test1pass = "Hello <!--world <!--inner--> text--> outside";
		string test1fail = "<!--Hello <!--world <!--inner--> text--> outside"; //unbalance delimeters, first
		//string test2pass = "Hello <!--world <!--inner--> text--> outside-->"; //unbalance delimeters, last
		Console.WriteLine(GetInnermostString(test1fail, "<!--", "-->")); // Outputs: "inner"
	}
	
}

 
using System;
​
public class Program
{
    public static string GetInnermostString(string input, string startDelimiter, string endDelimiter)
    {
        if (string.IsNullOrEmpty(input) || string.IsNullOrEmpty(startDelimiter) || string.IsNullOrEmpty(endDelimiter))
            return null;
​
        int innermostStart = -1;
        int innermostEnd = -1;
        int nestingLevel = 0;
        int maxNestingLevel = 0;
​
        for (int i = 0; i < input.Length - startDelimiter.Length + 1; i++)
        {
            if (input.Substring(i, startDelimiter.Length) == startDelimiter)
            {
                nestingLevel++;
                if (nestingLevel > maxNestingLevel)
                {
                    maxNestingLevel = nestingLevel;
                    innermostStart = i;
                }

Cached Result

Grok AI Generated Code for GetInnermostString function