13.罗马数字转成整形 Roman to Integer

public class Solution {
    public int RomanCharToInt(char c)
    {
        switch (c)
        {
            case ‘I‘:
                return 1;
            case ‘V‘:
                return 5;
            case ‘X‘:
                return 10;
            case ‘L‘:
                return 50;
            case ‘C‘:
                return 100;
            case ‘D‘:
                return 500;
            case ‘M‘:
                return 1000;
            default:
                return 0;
        }
    }
    public int RomanToInt(string s)
    {
        int length = s.Length;
        int i = length - 1;
        int sum = RomanCharToInt(s[i--]);
        while (i >= 0)
        {
            if (RomanCharToInt(s[i + 1]) > RomanCharToInt(s[i]))
            {
                sum -= RomanCharToInt(s[i--]);
            }
            else
            {
                sum += RomanCharToInt(s[i--]);
            }
        }
        return sum;
    }
}