[LeetCode] 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.

Solutions:

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