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

<p>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 <strong>any</strong> square that is an obstacle.</p>

<p>Return <em>the number of possible unique paths that the robot can take to reach the bottom-right corner</em>.</p>

<p>The testcases are generated so that the answer will be less than or equal to <code>2 * 10<sup>9</sup></code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0000-0099/0063.Unique%20Paths%20II/images/robot1.jpg" style="width: 242px; height: 242px;" />
<pre>
<strong>Input:</strong> obstacleGrid = [[0,0,0],[0,1,0],[0,0,0]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> 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>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0000-0099/0063.Unique%20Paths%20II/images/robot2.jpg" style="width: 162px; height: 162px;" />
<pre>
<strong>Input:</strong> obstacleGrid = [[0,1],[0,0]]
<strong>Output:</strong> 1
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<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>
Array; Dynamic Programming; Matrix
/**
 * @param {number[][]} obstacleGrid
 * @return {number}
 */
var uniquePathsWithObstacles = function (obstacleGrid) {
    const m = obstacleGrid.length;
    const n = obstacleGrid[0].length;
    const f = Array.from({ length: m }, () => Array(n).fill(-1));
    const dfs = (i, j) => {
        if (i >= m || j >= n || obstacleGrid[i][j] === 1) {
            return 0;
        }
        if (i === m - 1 && j === n - 1) {
            return 1;
        }
        if (f[i][j] === -1) {
            f[i][j] = dfs(i + 1, j) + dfs(i, j + 1);
        }
        return f[i][j];
    };
    return dfs(0, 0);
};
