Roman numerals to integers

Question

I have a transfer with products that unfortunately has to get matched by product name. The biggest issue here is I might get duplicate products on account of roman numbers.

Answer 1

Borrowed a lot from System.Linq on this one. String implements IEnumerable, so I figured that was appropriate since we are treating it as an enumerable object anyways. Tested it against a bunch of random numbers, including 1, 3, 4, 8, 83, 99, 404, 555, 846, 927, 1999, 2420.

    public static IDictionary CharValues 
    { 
        get 
        { 
            return new Dictionary
            {{'I', 1}, {'V', 5}, {'X', 10}, {'L', 50}, {'C', 100}, {'D', 500}, {'M', 1000}};
        } 
    }

    public static int RomanNumeralToInteger(IEnumerable romanNumerals)
    {
        int retVal = 0;

        //go backwards
        for (int i = romanNumerals.Count() - 1; i >= 0; i--)
        {
            //get current character
            char c = romanNumerals.ElementAt(i);

            //error checking
            if (!CharValues.ContainsKey(c)) throw new InvalidRomanNumeralCharacterException(c);

            //determine if we are adding or subtracting
            bool op = romanNumerals.Skip(i).Any(rn => CharValues[rn] > CharValues[c]);

            //then do so
            retVal = op ? retVal - CharValues[c] : retVal + CharValues[c];
        }

        return retVal;
    }