Unique Paths II

Problem

Follow up for "Unique Paths":
Now consider if some obstacles are added to the grids. How many unique paths would there be?
An obstacle and empty space is marked as 1 and 0 respectively in the grid.

For example,
There is one obstacle in the middle of a 3x3 grid as illustrated below.
[ [0,0,0], [0,1,0], [0,0,0] ]
The total number of unique paths is 2.
Note: m and n will be at most 100.

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Idea

dp，有点感觉了。dp[i][j]表示到grid[i][j]的unique path的数量. 需要注意的是如果grid[i][j]==1 那么dp[i][j]=0

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Solution

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