[LeetCode] Roman to Integer

class Solution {public:    int romanToInt(string s) {        map<char,int> m;        m['I'] = 1;        m['V'] = 5;        m['X'] = 10;        m['L'] = 50;        m['C'] = 100;        m['D'] = 500;        m['M'] = 1000;        int k = s.length() - 1;        int sum = m[s[k]];        while(k > 0){            if(m[s[k]] <= m[s[k - 1]])                sum += m[s[k - 1]];//从右往左计算，如果左边的大于右边则加上左边的数，否则减去左边的数。            else                sum -= m[s[k - 1]];            k --;        }        return sum;    }};