[LeetCode] Unique Paths II(DP)

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) {
        int rows = obstacleGrid.size();
        if(rows<1)
            return rows;
        int cols  = obstacleGrid[0].size();
        if(cols<1)
            return cols;
        vector<int> temp(cols,1);
        vector<vector<int> > res(rows,temp);//res记录到达相应位置的路径条数
        for(int i = 0;i<rows;i++){
            for(int j=0;j<cols;j++){
               if(obstacleGrid[i][j]==1)
                 res[i][j] = 0;
               else if(i==0 && j!=0)
                 res[i][j] = res[i][j-1];
               else if(j==0 && i!=0)
                 res[i][j] = res[i-1][j];
               else if(i!=0 && j!=0)
                 res[i][j] = res[i-1][j]+res[i][j-1];
            }
        
        }//end for
        return res[rows-1][cols-1];
    }
};