ou are given an m x n integer array grid. There is a robot initially located at the top$-$left corner $($i$.$e$.,$ grid$[0][0]).$ The robot tries to move to the bottom$-$right corner $($i$.$e$.,$ grid$[$m $-1][$n $-1]).$ The robot can only move either down or right at any point in time.

An obstacle and space are marked as $1$ or $0$ respectively in grid. A path that the robot takes cannot include any square that is an obstacle.

Return the number of possible unique paths that the robot can take to reach the bottom$-$right corner.

The testcases are generated so that the answer will be less than or equal to $2*109.$