> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Integer to Roman Python Solution with Tests

> Tested Python solution for LeetCode 12 with 20 pytest cases. Generate a practice environment with lcpy.

LeetCode 12, Medium. Topics: Hash Table, Math, String. [View on LeetCode](https://leetcode.com/problems/integer-to-roman/description/).

Generate this problem as a practice environment: tested reference solution, 20 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 12   # by problem number
lcpy gen -s integer_to_roman   # by problem name
```

## Problem

Seven different symbols represent Roman numerals with the following values:

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

Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules:

* If the value does not start with 4 or 9, select the symbol of the maximal value that can be subtracted from the input, append that symbol to the result, subtract its value, and convert the remainder to a Roman numeral.
* If the value starts with 4 or 9 use the **subtractive form** representing one symbol subtracted from the following symbol, for example, 4 is 1 (`I`) less than 5 (`V`): `IV` and 9 is 1 (`I`) less than 10 (`X`): `IX`. Only the following subtractive forms are used: 4 (`IV`), 9 (`IX`), 40 (`XL`), 90 (`XC`), 400 (`CD`) and 900 (`CM`).
* Only powers of 10 (`I`, `X`, `C`, `M`) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (`V`), 50 (`L`), or 500 (`D`) multiple times. If you need to append a symbol 4 times use the **subtractive form**.

Given an integer, convert it to a Roman numeral.

### Examples

```
Input: num = 3749
Output: "MMMDCCXLIX"

Explanation:

3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M)
 700 = DCC as 500 (D) + 100 (C) + 100 (C)
  40 = XL as 10 (X) less of 50 (L)
   9 = IX as 1 (I) less of 10 (X)
Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places
```

```
Input: num = 58
Output: "LVIII"

Explanation:

50 = L
 8 = VIII
```

```
Input: num = 1994
Output: "MCMXCIV"

Explanation:

1000 = M
 900 = CM
  90 = XC
   4 = IV
```

### Constraints

* `1 <= num <= 3999`

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/integer_to_roman/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/integer_to_roman/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(1)
    # Space: O(1)
    def int_to_roman(self, num: int) -> str:
        value_symbols: list[tuple[int, str]] = [
            (1000, "M"),
            (900, "CM"),
            (500, "D"),
            (400, "CD"),
            (100, "C"),
            (90, "XC"),
            (50, "L"),
            (40, "XL"),
            (10, "X"),
            (9, "IX"),
            (5, "V"),
            (4, "IV"),
            (1, "I"),
        ]

        result: list[str] = []
        for value, symbol in value_symbols:
            while num >= value:
                result.append(symbol)
                num -= value

        return "".join(result)
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(1) | O(1)  |

## Tags

[NeetCode All](/catalog/neetcode).