//Konwersja liczby arabskie <-> rzymskie
//www.algorytm.org
//(c)2007 Tomasz Lubinski

using System;

namespace rzymskie_cs
{
	/// <summary>
	/// Konwersja liczby arabskie <-> rzymskie
	/// </summary>
	class Rzymskie
	{
		private static int[] arabic = {1000, 500, 100, 50, 10, 5, 1};
		private static char[] roman = {'M', 'D', 'C', 'L', 'X', 'V', 'I'};
		private static int ROMAN_N = arabic.Length;

		/// <summary>
		/// Converts arabic <number> to roman <result>
		/// </summary>
		/// <param name="number">Arabic number to convert</param>
		/// <returns>Returns <result> or "", if an ERROR occurs.</returns>
		public static String arabic2roman(int number)
		{
			int i = 0; //position in arabic and roman arrays

			String result = "";

			if ((number > 3999) || (number <= 0))
			{
				return result;
			}

			while ((number > 0) && (i < ROMAN_N))
			{
				if(number >= arabic[i])
				{
					number -= arabic[i];
					result += roman[i];
				}
				else if ((i%2 == 0) &&
					(i<ROMAN_N-2) && // 9xx condition
					(number >= arabic[i] - arabic[i+2]) &&
					(arabic[i+2] != arabic[i] - arabic[i+2]))
				{
					number -= arabic[i] - arabic[i+2];
					result += roman[i+2];
					result += roman[i];
					i++;
				}
				else if ((i%2 == 1) &&
					(i<ROMAN_N-1) && //4xx condition
					(number >= arabic[i] - arabic[i+1]) &&
					(arabic[i+1] != arabic[i] - arabic[i+1]))
				{
					number -= arabic[i] - arabic[i+1];
					result += roman[i+1];
					result += roman[i];
					i++;
				}
				else
				{
					i++;
				}
			}

			return result;
		}

		/// <summary>
		/// Converts roman <number> to arabic
		/// </summary>
		/// <param name="number">Roman number to convert</param>
		/// <returns>Returns <result> or -1, if an ERROR occurs.</returns>
		public static int roman2arabic(String number)
		{
			int i = 0, //position in arabic and roman arrays
				j = 0, //position in number
				result = 0,
				length = 0;

			length = number.Length;

			while ((j<length) && (i<ROMAN_N))
			{
				if(number[j] == roman[i])
				{
					result += arabic[i];
					j++;
				}
				else if ((i%2 == 0) &&
					(i<ROMAN_N-2) && // 9xx condition
					(j<length-1) &&
					(number[j] == roman[i+2]) &&
					(number[j+1] == roman[i]))
				{
					result += arabic[i] - arabic[i+2];
					j += 2;
					i++;
				}
				else if ((i%2 == 1) &&
					(i<ROMAN_N-1) && //4xx condition
					(j<length-1) &&
					(number[j] == roman[i+1]) &&
					(number[j+1] == roman[i]))
				{
					result += arabic[i] - arabic[i+1];
					j += 2;
					i++;
				}
				else
				{
					i++;
				}
			}

			//there was an error during conversion
			if (i == ROMAN_N)
			{
				result = -1;
			}

			return result;
		}

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main(string[] args)
		{
		   String roman;

		   roman = arabic2roman(1981);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(1);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(3);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(4);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(5);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(6);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(45);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(68);
		   Console.WriteLine(roman2arabic(roman) + " = " +  roman);
		}
	}
}