// Unique Paths II — MEDIUM

// Category: dynamic-programming

A robot is located at the top-left corner of an `m x n` grid. The robot can only move right or down. Some cells contain obstacles (marked as `1`).

Return the number of unique paths from top-left to bottom-right.

**Constraint:** `obstacleGrid[i][j]` is 0 or 1.

Example: obstacleGrid = [[0,0,0],[0,1,0],[0,0,0]]

Output: 2