/// <summary>
/// finds and returns first duplicate character in string
/// </summary>
/// <param name="arr">array of items</param>
/// <returns>first duplicate item</returns>
public static char FindDuplicate(string str)
{
Tuple <string, char> result = ArrayProblems <char> .FindDuplicate(str.ToCharArray());
return(result.Item1 == "found" ? result.Item2 : ' ');
}
/// <summary>
/// reverses input string
/// </summary>
/// <param name="str">string - can be empty or one or more characters</param>
/// <returns>reversed string</returns>
public static string ReverseString(string str)
{
return(new string(ArrayProblems <char> .ReverseArray(str.ToCharArray())));
}