[LeetCode] Unique Paths 2

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.

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int m=obstacleGrid.size();
        int n=obstacleGrid[0].size();

        vector<vector<int>> paths(m,vector<int>(n,0));
        if(obstacleGrid.at(0).at(0)==1)
        {
            return 0;
        }
        else{
            paths.at(0).at(0)=1;
        }

        for(int i=1;i<m;i++)
        {
            if(obstacleGrid.at(i).at(0)==0 && paths.at(i-1).at(0)==1)
                paths.at(i).at(0)=1;
        }
        for(int i=1;i<n;i++)
        {
            if(obstacleGrid.at(0).at(i)==0 && paths.at(0).at(i-1)==1)
                paths.at(0).at(i)=1;
        }

        for(int i=1;i<m;i++)
        {
            for(int j=1;j<n;j++)
            {
                if(obstacleGrid.at(i).at(j)==1)
                    paths.at(i).at(j)=0;
                else
                    paths.at(i).at(j)=paths.at(i).at(j-1)+paths.at(i-1).at(j);
            }
        }  

        return paths.at(m-1).at(n-1);
    }
};