Roman to Integer

Roman to Integer (link)Jan 15 '12

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

class Solution {
    int romanToDigit(char c){
        int r = 0;
        switch(c){
            case 'I': r = 1; break;
            case 'V': r = 5; break;
            case 'X': r = 10; break;
            case 'L': r = 50; break;
            case 'C': r = 100; break;
            case 'D': r = 500; break;
            case 'M': r = 1000; break;                
        }
        return r;
    }
public:
    int romanToInt(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (s.empty()) return 0;
        int num = romanToDigit(s[s.length()-1]);
        int prev = num;
        for(int ii = s.length() - 2; ii >= 0; --ii){
            int const digitNum = romanToDigit(s[ii]);
            if (digitNum < prev) num -= digitNum;
            else num += digitNum;
            prev = digitNum;
        }
        return num;
    }
};