Leetcode: Integer to Roman and Roman to Integer

没什么可说的，纯刷题，
Integer to Roman，vector的建立可以单独写个API。
Roman to Integer，主要是规律找出来，如果后面的char比见面的大，就是相减得到res。

12. Integer to Roman
    https://leetcode.com/problems/integer-to-roman/description/

class Solution {
public:
    string intToRoman(int num) {
        vector<string> TH = {"", "M", "MM", "MMM"};
        vector<string> HU = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
        vector<string> TE = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
        vector<string> SI = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
        
        return (TH[num/1000] + HU[num % 1000 / 100] + TE[num % 100 / 10] + SI[num%10]);
    }
};

13. Roman to Integer
    https://leetcode.com/problems/roman-to-integer/description/

class Solution {
public:
    int romanToInt(string s) {
        unordered_map<char, int>map={
            {'I', 1},
            {'V', 5},
            {'X', 10},
            {'L', 50},
            {'C', 100},
            {'D', 500},
            {'M', 1000}
        };
        
        if(s.size() < 1) return 0;
        
        int res = map[s[0]];
        for(int i = 1; i < s.size(); i++)
        {
            if(map[s[i]] > map[s[i-1]])
            {
                res += map[s[i]] - 2*map[s[i-1]];
            }
            else
            {
                res += map[s[i]];
            }
        }
        
        return res;
    }
};