# LeetCode 12. Integer to Roman



Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`.

```
Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000
```

For example, `2` is written as `II` in Roman numeral, just two one's added together. `12` is written as `XII`, which is simply `X + II`. The number `27` is written as `XXVII`, which is `XX + V + II`.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not `IIII`. Instead, the number four is written as `IV`. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as `IX`. There are six instances where subtraction is used:

* `I` can be placed before `V` (5) and `X` (10) to make 4 and 9.&#x20;
* `X` can be placed before `L` (50) and `C` (100) to make 40 and 90.&#x20;
* `C` can be placed before `D` (500) and `M` (1000) to make 400 and 900.

Given an integer, convert it to a roman numeral.

**Example 1:**

```
Input: num = 3
Output: "III"
```

**Example 2:**

```
Input: num = 4
Output: "IV"
```

**Example 3:**

```
Input: num = 9
Output: "IX"
```

**Example 4:**

```
Input: num = 58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.
```

**Example 5:**

```
Input: num = 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
```

**Constraints:**

* `1 <= num <= 3999`

## Solution:

[English Version in Youtube](https://youtu.be/oL1hreAAFc0)

[中文版解答Youtube Link](https://youtu.be/d80x6Ruh1Ic)

[中文版解答Bilibili Link](https://www.bilibili.com/video/BV1bK4y1Q7mc/)

```
class Solution {
public:
    string intToRoman(int num) {
        map<int, string> mymap{
            {1, "I"}, {5, "V"}, {10, "X"}, {50, "L"},
            {100, "C"}, {500, "D"}, {1000, "M"},
            {4, "IV"}, {9, "IX"},
            {40, "XL"}, {90, "XC"},
            {400, "CD"}, {900, "CM"}
        };
        
        stringstream ss;
        for (auto it = mymap.rbegin(); it != mymap.rend(); it++) {
            int key = it->first;
            const string& code = it->second;
            while (num >= key) {
                num -= key;
                ss << code;
            }
        }
        
        return ss.str();
    }
};
```
