/// <summary>
/// Convert roman number to integer
/// </summary>
/// <returns>Integer</returns>
/// <param name="numberStr">Roman number</param>
public static int RomanToArabic(this string numberStr)
{
if (String.IsNullOrWhiteSpace(numberStr))
{
throw new ArgumentException("Invalid number provided.");
}
int res = 0;
bool isLastDigit = false;
bool skipNextDigit = false;
var chars = numberStr.ToCharArray();
for (int i = 0; i < chars.Count(); i++)
{
if (skipNextDigit)
{
skipNextDigit = false;
continue;
}
RomanNumberSymbol currentSymbol = GetRomanSymbol(chars.ElementAt(i));
isLastDigit = i == chars.Count() - 1;
int currentNumber = 0;
RomanNumberSymbol?nextSymbol = (isLastDigit) ? (RomanNumberSymbol?)null : GetRomanSymbol(chars.ElementAt(i + 1));
if (!isLastDigit && nextSymbol.HasValue && IsSpecialCase(currentSymbol, nextSymbol.Value))
{
currentNumber = (int)nextSymbol - (int)currentSymbol;
skipNextDigit = true;
}
else
{
currentNumber = (int)currentSymbol;
}
res += currentNumber;
}
return(res);
}
private static void AppendDigits(ref int number, RomanNumberSymbol romanDigit, StringBuilder str)
{
decimal digitsCount = number / (decimal)romanDigit;
if (digitsCount < 0)
{
return;
}
int subtrahend = (int)(Math.Floor(digitsCount) * (int)romanDigit);
number -= subtrahend;
int intCount = (int)Math.Floor(digitsCount);
for (int i = 0; i < intCount; i++)
{
str.Append(romanDigit.ToString());
}
}
private static bool IsSpecialCase(RomanNumberSymbol first, RomanNumberSymbol second)
{
if (first == second || first > second)
{
return(false);
}
if (first == RomanNumberSymbol.I && second == RomanNumberSymbol.V ||
first == RomanNumberSymbol.I && second == RomanNumberSymbol.X ||
first == RomanNumberSymbol.X && second == RomanNumberSymbol.L ||
first == RomanNumberSymbol.X && second == RomanNumberSymbol.C ||
first == RomanNumberSymbol.C && second == RomanNumberSymbol.D ||
first == RomanNumberSymbol.C && second == RomanNumberSymbol.M)
{
return(true);
}
throw new ArgumentException("Invalid Roman digit composition. Roman digits in numbers generally go from highest to lowest, " +
"only exception beeing 6 special cases when it's used for brevity, e.g. IV instead of IIII.");
}
