You are given a String input. You are to find the longest substring of input such that the reversal of the substring is also a substring of input. In case of a tie, return the string that occurs earliest in input.

Notes 
    -The substring and its reversal may overlap partially or completely. 
    -The entire original string is itself a valid substring (see example 4).
Constraints 
    -input will contain between 1 and 50 characters, inclusive. 
    -Each character of input will be an uppercase letter ('A'-'Z').
Examples
0) "XBCDEFYWFEDCBZ" 
    Returns: "BCDEF" 
    We see that the reverse of BCDEF is FEDCB, which appears later in the string.
1) "XYZ" 
    Returns: "X" 
    The best we can do is find a one character substring, so we implement the tie-breaker rule of taking the earliest one first.
2) "ABCABA" 
    Returns: "ABA" 
    The string ABA is a palindrome (it's its own reversal), so it meets the criteria.
3) "FDASJKUREKJFDFASIREYUFDHSAJYIREWQ" 
    Returns: "FDF"
    The similar as above.
4) "ABCDCBA" 
    Returns: "ABCDCBA" 
    Here, the entire string is its own reversal.

class ReverseSubstring
{
    static void Main(string[] args)
    {
        string[] strings = new string[] { "XBCDEFYWFEDCBZ", "XYZ", 
                "FDASJKUREKJFDFASIREYUFDHSAJYIREWQ", "ABCDCBA" };
        for ( int i=0 ; i < strings.Length ; ++i )
        {
            System.Console.WriteLine(FindReversed(strings[i]));
        }
    }

    private static string FindReversed(string input)
    {
        string substring = string.Empty;
        for ( int i=0 ; i < input.Length ; ++i )
        {
            for ( int j=0 ; j < input.Length ; ++j )
            {
                if ( input[i] == input[input.Length-1-j] )
                {
                    if ( i == input.Length-1-j )
                    {
                        if ( substring.Length == 0 )
                        {
                            substring = input[i].ToString();
                        }
                        break;
                    }
                    else
                    {
                        int k = 0;
                        for ( ; k < input.Length-i-j ; ++k )
                        {
                            if ( input[i+k] != input[input.Length-1-j-k] ) break;
                        }
                        if ( substring.Length < k )
                        {
                            substring = input.Substring(i, k);
                        }
                    }
                }
            }
        }
        return substring;
    }
}

BCDEF
X
ABA
FDF
ABCDCBA