罗马数字转化为整数（1~3999）

Given a roman numeral, convert it to an integer.

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

class Solution {
public:
    int romanToInt(string s) {
        if(s.size() == 0) return 0;
        int num=0;
        for(size_t i=0;i=0 && s[i-1] == 'I')?num+3:num+5;
                        break;
                    case 'X':
                        num=(i-1>=0 && s[i-1] == 'I') ? num+8 : num+10;
                        break;
                    case 'L':
                        num=(i-1>=0 && s[i-1] == 'X') ? num+30 : num+50;
                        break;
                    case 'C':
                        num=(i-1>=0 && s[i-1] == 'X') ? num+80 : num+100;
                        break;
                    case 'D':
                        num=(i-1>=0 && s[i-1] == 'C') ? num+300 : num+500;
                        break;
                    case 'M':
                        num=(i-1>=0 && s[i-1] == 'C') ? num+800 : num+1000;
                        break;
                    default: break;
            }
        }
        if(num >3999) return 0;
        return num;
    }
};