https://leetcode.com/problems/unique-paths-ii/

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

Now consider if some obstacles are added to the grids. How many unique paths would there be?

An obstacle and empty space is marked as 1 and 0 respectively in the grid.

Note: m and n will be at most 100.

Example 1:

Input:
[
  [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

程式碼：

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        int m = obstacleGrid.size(), n = obstacleGrid[0].size();
        if(obstacleGrid[0][0] == 1) return 0;
        vector<int> dp(n, 0);
        dp[0] = 1;
        for(int i = 0; i < m; i ++) {
            for(int j = 0; j < n; j ++) {
                if(obstacleGrid[i][j] == 1) dp[j] = 0;
                else dp[j] += dp[j - 1];
            }
        }
        return dp[n - 1];
    }
};

$m$ 行 $n$ 列真的是寫不習慣 這個只多了一個是 $1$ 的時候走不動 那就到該點的時候 $dp$ 設成 $0$ 就好了 本來想用深搜搜路徑數量但是。。。很難受寫錯了。。。晚上回去再好好擼 $dfs$ 吧