【leetcode】 Unique Path ||(easy)

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.

思路：跟Unique Paths差不多，就是把有障碍的地方方法数变成0，注意左上角为障碍的情况

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        if(obstacleGrid.empty())
        {
            return 0;
        }
        vector<vector<int>> ways(obstacleGrid.size(), vector<int>(obstacleGrid[0].size(),1));
        if(obstacleGrid[0][0] == 1)
        {
            ways[0][0] = 0;
        }
        for(int c = 1; c < obstacleGrid[0].size(); c++)
        {
            ways[0][c] = (obstacleGrid[0][c] == 1) ? 0 : ways[0][c - 1];
        }
        for(int r = 1; r < obstacleGrid.size(); r++)
        {
            ways[r][0] = (obstacleGrid[r][0] == 1) ? 0 : ways[r - 1][0];
        }
        for(int i = 1; i < obstacleGrid.size(); i++)
        {
            for(int j = 1; j < obstacleGrid[0].size(); j++)
            {
                ways[i][j] = (obstacleGrid[i][j] == 1) ? 0 : ways[i - 1][j] + ways[i][j - 1];
            }
        }
        return ways[obstacleGrid.size() - 1][obstacleGrid[0].size() - 1];
    }
};