leetcode Question 117: Unique Path II

Unique Path 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.
The total number of unique paths is 2.

Just a little bit changes from the previous problem.
Note that if the start position is obstacle, then return 0.
Pretty easy if you solve the previous one.

class Solution {
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int m = obstacleGrid.size();
        int n = obstacleGrid[0].size();
        vector<vector<int> > arr(m,vector<int>(n,0));
        if (obstacleGrid[0][0]==1){return 0;}
        for (int i=1;i<m;i++){
            if (obstacleGrid[i][0]!=1){
                arr[i][0] = arr[i-1][0];
        for (int i=1;i<n;i++){
            if (obstacleGrid[0][i]!=1){
                arr[0][i] = arr[0][i-1];
        for (int i=1;i<m;i++){
            for(int j=1;j<n;j++){
                if (obstacleGrid[i][j]!=1){
                    arr[i][j] = arr[i][j-1] + arr[i-1][j];
        return arr[m-1][n-1];

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