# 12. Integer to Roman

[Link](https://leetcode.com/problems/roman-to-integer/)

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

**Example 1:**

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

**Example 2:**

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

**Example 3:**

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

**Example 4:**

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

**Example 5:**

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

**Solution**

```
  public String intToRoman(int num) {
        StringBuilder sb = new StringBuilder();
        int i = num / 1000;
        while (i != 0) {
            sb.append("M");
            i--;
        }
        num = num % 1000;
        if (num >= 900) {
            num -= 900;
            sb.append("CM");
        }
        if (num >= 500) {
            num -= 500;
            sb.append("D");
        }
        if (num >= 400) {
            num -= 400;
            sb.append("CD");
        }
        i = num / 100;
        while (i != 0) {
            sb.append("C");
            i--;
        }
        num = num % 100;
        if(num >= 90){
            num -= 90;
            sb.append("XC");
        }
        if(num >= 50){
            num -= 50;
            sb.append("L");
        }
        if(num >= 40){
            num -= 40;
            sb.append("XL");
        }
        i = num / 10;
        while (i != 0) {
            sb.append("X");
            i--;
        }
        num = num % 10;
        if(num >= 9){
            num -= 9;
            sb.append("IX");
        }
        if(num >= 5){
            num -= 5;
            sb.append("V");
        }
        if(num >= 4){
            num -= 4;
            sb.append("IV");
        }
        while (num != 0) {
            sb.append("I");
            num--;
        }
        return sb.toString();
    }
```
