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.

代码：

    vector<vector<int> >result;
    int search(int sx, int sy, int ex, int ey, vector<vector<int> > &obstacleGrid){
        if(sx > ex || sy > ey || obstacleGrid[sx][sy] == 1)
            return 0;
        if(result[sx][sy] != -1)
            return result[sx][sy];
        if(sx == ex && sy == ey)
            return 1;
        result[sx][sy] = search(sx+1, sy, ex, ey, obstacleGrid) + search(sx, sy+1, ex, ey, obstacleGrid);
        return result[sx][sy];
    }
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        result.clear();
        int m = obstacleGrid.size();
        if(m == 0)
            return 0;
        int n = obstacleGrid[0].size();
        if(n == 0)
            return 0;
        int i,j;
        for(i = 0; i < m; i++){
            vector<int> tmp(n, -1);
            result.push_back(tmp);
        }
        return search(0, 0, m-1, n-1, obstacleGrid);
    }