> ## 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.

# Unique Paths II Python Solution with Tests

> Tested Python solution for LeetCode 63 with 12 pytest cases. Generate a practice environment with lcpy.

LeetCode 63, Medium. Topics: Array, Dynamic Programming, Matrix. [View on LeetCode](https://leetcode.com/problems/unique-paths-ii/description/).

Generate this problem as a practice environment: tested reference solution, 12 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 63   # by problem number
lcpy gen -s unique_paths_ii   # by problem name
```

## Problem

You are given an `m x n` integer array `grid`. There is a robot initially located at the **top-left corner** (i.e., `grid[0][0]`). The robot tries to move to the **bottom-right corner** (i.e., `grid[m - 1][n - 1]`). The robot can only move either down or right at any point in time.

An obstacle and space are marked as `1` or `0` respectively in `grid`. A path that the robot takes cannot include any square that is an obstacle.

Return *the number of possible unique paths that the robot can take to reach the bottom-right corner*.

### Examples

```
Input: obstacleGrid = [[0,0,0],[0,1,0],[0,0,0]]
Output: 2

Explanation: There is one obstacle in the middle of the 3x3 grid above.
There are two ways to reach the bottom-right corner:
1. Right -> Right -> Down -> Down
2. Down -> Down -> Right -> Right
```

```
Input: obstacleGrid = [[0,1],[0,0]]
Output: 1
```

### Constraints

* `m == obstacleGrid.length`
* `n == obstacleGrid[i].length`
* `1 <= m, n <= 100`
* `obstacleGrid[i][j] is 0 or 1`

## Solution

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

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(m * n)
    # Space: O(n)
    def unique_paths_with_obstacles(self, grid: list[list[int]]) -> int:
        m, n = len(grid), len(grid[0])
        if grid[0][0] == 1 or grid[m - 1][n - 1] == 1:
            return 0

        dp = [0] * n
        dp[0] = 1
        for i in range(m):
            for j in range(n):
                if grid[i][j] == 1:
                    dp[j] = 0
                elif j > 0:
                    dp[j] += dp[j - 1]
        return dp[n - 1]
```

## Complexity

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

## Tags

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