# [Integer to Roman][title]

## Description

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, two is written as `II` in Roman numeral, just two one's added together. Twelve is written as, `XII`, which is simply `X` + `II`. The number twenty seven 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. 
- `X` can be placed before `L` (50) and `C` (100) to make 40 and 90. 
- `C` can be placed before `D` (500) and `M` (1000) to make 400 and 900.

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

**Example 1:**

```
Input: 3
Output: "III"
```

**Example 2:**

```
Input: 4
Output: "IV"
```

**Example 3:**

```
Input: 9
Output: "IX"
```

**Example 4:**

```
Input: 58
Output: "LVIII"
Explanation: C = 100, L = 50, XXX = 30 and III = 3.
```

**Example 5:**

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

**Tags:** Math, String


## 思路

题意是整型数转罗马数字，范围从 1 到 3999，查看下百度百科的罗马数字介绍如下：

* 相同的数字连写，所表示的数等于这些数字相加得到的数，如 Ⅲ=3；

* 小的数字在大的数字的右边，所表示的数等于这些数字相加得到的数，如 Ⅷ=8、Ⅻ=12；

* 小的数字（限于 Ⅰ、X 和 C）在大的数字的左边，所表示的数等于大数减小数得到的数，如 Ⅳ=4、Ⅸ=9。

那么我们可以把整数的每一位分离出来，让其每一位都用相应的罗马数字位表示，最终拼接完成。比如 `621` 我们可以分离百、十、个分别为 `6`、`2`、`1`，那么 `600` 对应的罗马数字是 `DC`，`20` 对应的罗马数字是 `XX`，`1` 对应的罗马数字是 `I`，所以最终答案便是 `DCXXI`。

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


## 结语

如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-java-leetcode][ajl]



[title]: https://leetcode.com/problems/integer-to-roman
[ajl]: https://github.com/Blankj/awesome-java-leetcode