namespace Iteration;

public class Recursion
{
    public static bool IsAlphanum(string s, int i)
    {
        if (i >= s.Length)
        {
            return true;
        }
        else
        {
            if ((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z') || (s[i] >= '0' && s[i] <= '9'))
            {
                return IsAlphanum(s, i + 1);
            }
            else
            {
                return false;
            }
        }
    }

    public static string ReverseStr(string source, int lenght)
    {
        if (lenght == 0)
        {
            return "";
        }
        else
        {
            return source[lenght - 1] + ReverseStr(source, lenght - 1);
        }
    }
}