leetcode: 63. Unique Paths II

Q

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.

AC

class Solution(object):    def uniquePathsWithObstacles(self, obstacleGrid):        """        :type obstacleGrid: List[List[int]]        :rtype: int        """        m, n = len(obstacleGrid), len(obstacleGrid[0])        ways = [0]*n        ways[0] = 1        for i in xrange(m):            if obstacleGrid[i][0] == 1:                ways[0] = 0            for j in xrange(n):                if obstacleGrid[i][j] == 1:                    ways[j] = 0                elif j>0:                    ways[j] += ways[j-1]        return ways[-1]# Time:  O(m * n)# Space: O(m + n)class Solution2(object):    def uniquePathsWithObstacles(self, obstacleGrid):        """        :type obstacleGrid: List[List[int]]        :rtype: int        """        m, n = len(obstacleGrid), len(obstacleGrid[0])        ways = [0]*n        ways[0] = 1        for i in xrange(m):            if obstacleGrid[i][0] == 1:                ways[0] = 0            for j in xrange(n):                if obstacleGrid[i][j] == 1:                    ways[j] = 0                elif j>0:                    ways[j] += ways[j-1]        return ways[-1]if __name__ == "__main__":    obstacleGrid = [        [0,0,0],        [0,1,0],        [0,0,0]    ]    assert Solution().uniquePathsWithObstacles(obstacleGrid) == 2

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