using System;

public class Program

{

    public static void Main()

    {

        Program lps = new Program();

            string sInput = "babad";

            string sAnswer = lps.LongestPalindromicSubstring(sInput);

            Console.WriteLine("The answer is: " + sAnswer);       

    }

    public string LongestPalindromicSubstring(string sInput)

        {

            //char[] caInput = sInput.ToCharArray();

            int iLongestPalindromicSubstring = 0;

            string sLongestPalindromicSubstring = "";

​

            for (int j = sInput.Length; j > 0; j--)

            {

                for (int i = 0; i < sInput.Length; i++)

                {

                    if ( j - i >= 0)

                    {

                        //Console.Read();

                        //Console.WriteLine("i is: " + i + " j is: " + (j - i));

​

                        string sInputSubstring = sInput.Substring(i, j - i);

​

                        Console.WriteLine(sInputSubstring);

​

                        if (CheckPalindromicString(sInputSubstring))

                        {

                            if (iLongestPalindromicSubstring < sInputSubstring.Length)

                            {

                                iLongestPalindromicSubstring = sInputSubstring.Length;

                                sLongestPalindromicSubstring = sInputSubstring;

                            }

​

                            //Console.WriteLine(iLongestPalindromicSubstring);

                            //Console.WriteLine(sLongestPalindromicSubstring);

                        }

                    }

                }

            }

​

            return (sLongestPalindromicSubstring);

        }

​

        private bool CheckPalindromicString(string sPalindromicString)

        {

            string sReverseString = "";

            char[] caPalindromicString = sPalindromicString.ToCharArray();

            char[] caReverseString = new char[sPalindromicString.Length];

​

            for (int i = 0; i < caPalindromicString.Length; i++)

            {                

                caReverseString[i] = caPalindromicString[(caPalindromicString.Length - 1) - i];

            }

​

            sReverseString = new string(caReverseString);

​

            //Console.WriteLine(sPalindromicString);

            //Console.WriteLine(caReverseString);

​

            bool bIsPalindromicString = sReverseString == sPalindromicString ? true : false;

​

            return bIsPalindromicString;

        }

}