63. Unique Paths II 解题记录

题目描述：

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.

解题思路：

这题的思路和上一题还是大致相同的，只是这题多了障碍。不过没关系，遇到障碍说明那条路走不通，path为0，所以每次相加时只要把判断一下是否遇到障碍就可以了。还有就是要是起点或终点被障碍堵了，直接回0。

代码：

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        int col = obstacleGrid[0].size(), row = obstacleGrid.size();
        if(obstacleGrid[0][0] == 1 || obstacleGrid[row-1][col-1] == 1)
            return 0;
        vector<int> ret(col+1, 0);
        ret[1] = 1;
        for(int i = 0; i < row; i++){
            for(int j = 0; j < col; j++){
                if(obstacleGrid[i][j] == 1)
                    ret[j+1] = 0;
                else
                    ret[j+1] += ret[j];
            }
        }
        return ret[col];
    }
};