> ## 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.

# Multiply Strings Python Solution with Tests

> Tested Python solution for LeetCode 43 with 16 pytest cases. Generate a practice environment with lcpy.

LeetCode 43, Medium. Topics: Math, String, Simulation. [View on LeetCode](https://leetcode.com/problems/multiply-strings/description/).

Generate this problem as a practice environment: tested reference solution, 16 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 43   # by problem number
lcpy gen -s multiply_strings   # by problem name
```

## Problem

Given two non-negative integers `num1` and `num2` represented as strings, return the product of `num1` and `num2`, also represented as a string.

**Note:** You must not use any built-in BigInteger library or convert the inputs to integer directly.

### Examples

```
Input: num1 = "2", num2 = "3"
Output: "6"
```

```
Input: num1 = "123", num2 = "456"
Output: "56088"
```

### Constraints

* 1 \<= num1.length, num2.length \<= 200
* `num1` and `num2` consist of digits only.
* Both `num1` and `num2` do not contain any leading zero, except the number `0` itself.

## Solution

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

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(m * n)
    # Space: O(m + n)
    def multiply(self, num1: str, num2: str) -> str:
        if num1 == "0" or num2 == "0":
            return "0"
        m, n = len(num1), len(num2)
        result = [0] * (m + n)
        for i in range(m - 1, -1, -1):
            for j in range(n - 1, -1, -1):
                product = (ord(num1[i]) - ord("0")) * (ord(num2[j]) - ord("0"))
                total = product + result[i + j + 1]
                result[i + j + 1] = total % 10
                result[i + j] += total // 10
        return "".join(str(x) for x in result).lstrip("0")
```

## Complexity

| Time      | Space    |
| --------- | -------- |
| O(m \* n) | O(m + n) |

## Tags

[NeetCode 150](/catalog/neetcode-150), [NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).