13 罗马数字转整数

https://leetcode.cn/leetbook/read/top-interview-questions-easy/xn4n7c/

https://leetcode.cn/problems/roman-to-integer/

cost: 10m21s

class Solution {
public:
    int romanToInt(string str) {
        int r = 0;
        int n = str.size();
        for (int i = 0; i < n; i++) {
            char ch = str[i];
            switch (ch) {
            case 'I':
                if (i < n && str[i + 1] == 'V' || str[i + 1] == 'X') {
                    r -= 1;
                } else {
                    r += 1;
                }
                break;
            case 'V':
                r += 5;
                break;
            case 'X':
                if (i < n && str[i + 1] == 'L' || str[i + 1] == 'C') {
                    r -= 10;
                } else {
                    r += 10;
                }
                break;
            case 'L':
                r += 50;
                break;
            case 'C':
                if (i < n && str[i + 1] == 'D' || str[i + 1] == 'M') {
                    r -= 100;
                } else {
                    r += 100;
                }
                break;
            case 'D':
                r += 500;
                break;
            case 'M':
                r += 1000;
                break;
            }
        }
        return r;
    }
};