public virtual int ToDecimal()
{
if (!IsValid())
{
throw new Exception("Invalid number: " + this);
}
int result = 0;
for (int i = 0; i < symbols.Length; i++)
{
RomanSymbol currentSymbol = symbols[i];
if (i < symbols.Length - 1)
{
RomanSymbol nextSymbol = symbols[i + 1];
if (nextSymbol.Value() > currentSymbol.Value())
{
result -= currentSymbol.Value();
}
else
{
result += currentSymbol.Value();
}
}
else
{
result += currentSymbol.Value();
}
}
return(result);
}
private bool IsValidSubtraction(int i, RomanSymbol currentSymbol)
{
if (i < symbols.Length - 1)
{
//V,D,L can't subtract nothing
if (new[] { "V", "D", "L" }.Contains(currentSymbol.Literal))
{
for (int j = i + 1; j < symbols.Length; j++)
{
if (symbols[j].Value() > currentSymbol.Value())
{
return(false);
}
}
}
//Nothing can subtract and add right after : IXI, IXII, IXIII is invalid
if (i < symbols.Length - 2 && symbols[i + 1].Value() > currentSymbol.Value() && symbols[i + 2].Value() >= currentSymbol.Value())
{
return(false);
}
//Can't add to subtract. Ex: IIX,IIIX,XXC,XXXC ...
if (symbols[i + 1].Equals(currentSymbol))
{
for (int j = i + 1; j < symbols.Length; j++)
{
if (symbols[j].Value() > currentSymbol.Value())
{
return(false);
}
}
}
}
//I can only subtract X
if (currentSymbol.Literal.Equals("I"))
{
if (i < symbols.Length - 1 && new[] { "D", "C", "M", "L" }.Contains(symbols[i + 1].Literal))
{
return(false);
}
}
//X can only subtract C
if (currentSymbol.Literal.Equals("X"))
{
if (i < symbols.Length - 1 && new[] { "D", "M" }.Contains(symbols[i + 1].Literal))
{
return(false);
}
}
return(true);
}