class Solution {
public:
        int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) 
        {
                int m=obstacleGrid.size();
                int n=obstacleGrid[0].size();
                
                if(obstacleGrid[0][0]==1) // initial point has a obstacle base case
                        return 0;
                
                vector<vector<int>> dp(m, vector<int> (n,0));
                for(int i=0;i<m;i++)
                {
                        if(obstacleGrid[i][0])  // can not reach any further point from here
                                break;
                        else
                                dp[i][0]=1;
                }
                for(int j=0;j<n;j++)
                {
                        if(obstacleGrid[0][j])  // can not reach any further point from here
                                break;
                        else
                                dp[0][j]=1;
                }
                
                for(int i=1;i<m;i++)
                {
                        for(int j=1;j<n;j++)
                        {
                                if(!obstacleGrid[i][j])
                                        dp[i][j]=dp[i-1][j]+dp[i][j-1];     // number of ways = no of ways to reach i,j-1 + no of ways to reach i-1,j 
                        }
                }
                return dp[m-1][n-1];
        }
};