63. Unique Paths II

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.

思路：将两边和1初始化即可。

class Solution:    def uniquePathsWithObstacles(self, obstacleGrid):        """        :type obstacleGrid: List[List[int]]        :rtype: int        """        if obstacleGrid[-1][-1]==1 or obstacleGrid[0][0]==1:            return 0        m,n=len(obstacleGrid),len(obstacleGrid[0])        dp=[[0]*n for i in range(m)]        for j in range(n):            if obstacleGrid[0][j]==0:                dp[0][j]=1            else:                for jj in range(j,n):                    dp[0][jj]=0                break        for i in range(m):            if obstacleGrid[i][0]==0:                dp[i][0]=1            else:                for ii in range(i,m):                    dp[ii][0]=0                break        for i in range(1,m):            for j in range(1,n):                    dp[i][j]=dp[i-1][j]+dp[i][j-1] if obstacleGrid[i][j]!=1 else 0        return dp[-1][-1]