> For the complete documentation index, see [llms.txt](https://hao-fu-1.gitbook.io/oj/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hao-fu-1.gitbook.io/oj/math/roman-to-integer.md).

# Roman to Integer

<https://leetcode.com/problems/roman-to-integer/description/>

> Given a roman numeral, convert it to an integer.
>
> Input is guaranteed to be within the range from 1 to 3999.

## Thoughts

背下来好了...

## Code

```
class Solution {
    public int romanToInt(String s) {
        int sum = 0;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch(c) {
                case 'M':
                    sum += 1000;
                    break;
                case 'D':
                    sum += 500;
                    break;
                case 'C':
                    sum += 100;
                    break;
                case 'L':
                    sum += 50;
                    break;
                case 'X':
                    sum += 10;
                    break;
                case 'V':
                    sum += 5;
                    break;
                default:
                    sum += 1;
            }
        }

        if(s.indexOf("IV")!=-1){sum-=2;}
        if(s.indexOf("IX")!=-1){sum-=2;}
        if(s.indexOf("XL")!=-1){sum-=20;}
        if(s.indexOf("XC")!=-1){sum-=20;}
        if(s.indexOf("CD")!=-1){sum-=200;}
        if(s.indexOf("CM")!=-1){sum-=200;}

        return sum;
    }
}
```

## Analysis

时空复杂度O(N).