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Kotlin-based LeetCode algorithm problem solutions, regularly updated
63\. Unique Paths II
Medium
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_.
The testcases are generated so that the answer will be less than or equal to 2 * 109
.
**Example 1:**
![](https://assets.leetcode.com/uploads/2020/11/04/robot1.jpg)
**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
**Example 2:**
![](https://assets.leetcode.com/uploads/2020/11/04/robot2.jpg)
**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`.