Unique Paths II

public class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
         if(obstacleGrid == null || obstacleGrid.length==0 || obstacleGrid[0].length==0)  return 0;
 
    int[] res= new int[ obstacleGrid[0].length];
    res[0]=1;
    for(int i=0; i< obstacleGrid.length; i++){
        for(int j=0; j< obstacleGrid[0].length;j++){
            if(obstacleGrid[i][j]==1){
                res[j]=0;
            }else{ 
                if(j>0)
                    res[j] += res[j-1];
            }
            
        }
    }
    return res[ obstacleGrid[0].length-1];
    
    }
}