//Konwersja liczby arabskie <-> rzymskie
//www.algorytm.org
//(c)2006 Tomasz Lubinski
public class Rzymskie {

	private static final int arabic[] = {1000, 500, 100, 50, 10, 5, 1};
	private static final char roman[] = {'M', 'D', 'C', 'L', 'X', 'V', 'I'};
	private static final int ROMAN_N = arabic.length;
	
	//Converts arabic <number> to roman <result>
	//Returns <result> or "", if an ERROR occurs.
	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;
	}	
	
	//Converts roman <number> to arabic
	//Returns <result> or -1, if an ERROR occurs.
	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.charAt(j) == roman[i])
	        {
	            result += arabic[i];
	            j++;
	        }
	        else if ((i%2 == 0) &&
	                 (i<ROMAN_N-2) && // 9xx condition
	                 (j<length-1) &&
	                 (number.charAt(j) == roman[i+2]) &&
	                 (number.charAt(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.charAt(j) == roman[i+1]) &&
	                 (number.charAt(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;
	}
	
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		   String roman;

		   roman = arabic2roman(1981);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(1);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(3);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(4);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(5);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(6);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(45);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
		   roman = arabic2roman(68);
		   System.out.println(roman2arabic(roman) + " = " +  roman);
	}

}