Unique Paths II

Follow up for "Unique Paths":
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.
For example,
There is one obstacle in the middle of a 3x3 grid as illustrated below.
[
[0,0,0],
[0,1,0],
[0,0,0]
]
The total number of unique paths is 2.
Note: m and n will be at most 100.

Solution: Dynamic programming.

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