Leetcode 63. 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.

class Solution {public:    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {        size_t rows = obstacleGrid.size();        size_t cols = obstacleGrid[0].size();        vector<int> p(rows, 0);        p[0] = 1;        for (size_t i = 0; i != cols; ++i) {            if (obstacleGrid[0][i] == 1)                p[0] = 0;            else                 p[0] = p[0];            for (size_t j = 1; j !=rows; ++j){                if (obstacleGrid[j][i] == 1)                    p[j] = 0;                else                    p[j] = p[j] + p[j - 1];            }        }        return p[rows - 1];    }};