> For the complete documentation index, see [llms.txt](https://dfine.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dfine.gitbook.io/leetcode/13.roman_to_integer.md).

# 13.Roman to Integer

\#13.Roman to Integer 难度:Easy

> 罗马数字包含以下七种字符: I， V， X， L，C，D 和 M。

```
字符          数值
I             1
V             5
X             10
L             50
C             100
D             500
M             1000
例如， 罗马数字 2 写做 II ，即为两个并列的 1。12 写做 XII ，即为 X + II 。 27 写做  XXVII, 即为 XX + V + II 。

通常情况下，罗马数字中小的数字在大的数字的右边。但也存在特例，例如 4 不写做 IIII，而是 IV。数字 1 在数字 5 的左边，所表示的数等于大数 5 减小数 1 得到的数值 4 。同样地，数字 9 表示为 IX。这个特殊的规则只适用于以下六种情况：

I 可以放在 V (5) 和 X (10) 的左边，来表示 4 和 9。
X 可以放在 L (50) 和 C (100) 的左边，来表示 40 和 90。 
C 可以放在 D (500) 和 M (1000) 的左边，来表示 400 和 900。
给定一个罗马数字，将其转换成整数。输入确保在 1 到 3999 的范围内。

示例 1:

输入: "III"
输出: 3
示例 2:

输入: "IV"
输出: 4
示例 3:

输入: "IX"
输出: 9
示例 4:

输入: "LVIII"
输出: 58
解释: L = 50, V= 5, III = 3.
示例 5:

输入: "MCMXCIV"
输出: 1994
解释: M = 1000, CM = 900, XC = 90, IV = 4.
```

方法:

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


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