unique-paths-ii

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Algorithms

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

An obstacle and space are marked as <code>1</code> or <code>0</code> respectively in <code>grid</code>. 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 <code>2 * 109</code>.

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/04/robot1.jpg" style="width: 242px; height: 242px;" />
<pre>
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 -&gt; Right -&gt; Down -&gt; Down
2. Down -&gt; Down -&gt; Right -&gt; Right
</pre>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/04/robot2.jpg" style="width: 162px; height: 162px;" />
<pre>
Input: obstacleGrid = [[0,1],[0,0]]
Output: 1
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>m == obstacleGrid.length</code></li>
	<li><code>n == obstacleGrid[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 100</code></li>
	<li><code>obstacleGrid[i][j]</code> is <code>0</code> or <code>1</code>.</li>
</ul>