# [63. Unique Paths II](https://leetcode.com/problems/unique-paths-ii/)


## 题目

A robot is located at the top-left corner of a *m* x *n* grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

Now consider if some obstacles are added to the grids. How many unique paths would there be?

![](https://assets.leetcode.com/uploads/2018/10/22/robot_maze.png)

An obstacle and empty space is marked as `1` and `0` respectively in the grid.

**Note:** *m* and *n* will be at most 100.

**Example 1:**

    Input:
    [
      [0,0,0],
      [0,1,0],
      [0,0,0]
    ]
    Output: 2
    Explanation:
    There is one obstacle in the middle of the 3x3 grid above.
    There are two ways to reach the bottom-right corner:
    1. Right -> Right -> Down -> Down
    2. Down -> Down -> Right -> Right

## 题目大意

一个机器人位于一个 m x n 网格的左上角 （起始点在下图中标记为“Start” ）。机器人每次只能向下或者向右移动一步。机器人试图达到网格的右下角（在下图中标记为“Finish”）。现在考虑网格中有障碍物。那么从左上角到右下角将会有多少条不同的路径？


## 解题思路

- 这一题是第 62 题的加强版。也是一道考察 DP 的简单题。
- 这一题比第 62 题增加的条件是地图中会出现障碍物，障碍物的处理方法是 `dp[i][j]=0`。
- 需要注意的一种情况是，起点就是障碍物，那么这种情况直接输出 0 。