罗马数字转换成整数

方法一：

class Solution {
public:
    int romanToInt(string s) {
        
        int len=s.size();
        map<string,int> number{
            {"I",1},
            {"V",5},
            {"X",10},
            {"L",50},
            {"C",100},
            {"D",500},
            {"M",1000},
            {"IV",4},
            {"IX",9},
            {"XL",40},
            {"XC",90},
            {"CD",400},
            {"CM",900}
        };
        
        string s1;
        string s2;
        string s3;
        int sum=0;
        int i=0;
        for(i;i<=len-2;)
        {
            s1=s.substr(i,1);
            s2=s.substr(i+1,1);
            if(number.at(s1)<number.at(s2))
            {
                s3=s1+s2;
                sum=number.at(s3)+sum;
                i=i+2;
            }
            else
            {
                sum=number.at(s1)+sum;
                i++;
            }
            
        }
        if(i==len-1)
        {
            sum=number.at(s.substr(len-1,1))+sum;
        }
        
        return sum;
    }
};