fromRomanToDec

fromRomanToDec.java

    private static int toDecimal(final String roman)
    {
        String[] chars = roman.split("(?!^)");

        int d = 0;
        ROMAN last = null;
        // the trick is run the sequence from right to left
        for (int i = chars.length - 1; i >= 0; i--)
        {
            String c = chars[i];
            ROMAN r = ROMAN.valueOf(c.toUpperCase());
            
            // ordrinal returns the index as declared in enum, p.e: I=0,V=1,X=3
            // so we can know if a char has a greater value than an other
            // then:
            
            // if last char is lower than actual, we keep using adding the value
            if (last == null || last.ordinal() <= r.ordinal())
            {
                d += r.decimal;
            }
            // if the last bigger than the actual, we substract its value,
            // p.e: IX -> last = X and actual = I -> X - I
            else
            {
                d -= r.decimal;
            }
            last = r;
        }

        return d;
    }

    enum ROMAN
    {
        I(1), V(5), X(10), L(50), C(100), D(500), M(1000);

        final int decimal;

        private ROMAN(final int decimal)
        {
            this.decimal = decimal;
        }
    }