63. Unique Paths II【M】【30】

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.

Subscribe to see which companies asked this question

与之前的unique path 很像，就是需要对每一个砖进行判断，而且初始化也需要重新写

class Solution(object):
    def uniquePathsWithObstacles(self, obstacleGrid):
        x = obstacleGrid
        m = len(x)
        n = len(x[0])

        r1 = [0] * n
        r2 = [0] * n
        for i in xrange(len(r1)):
            if x[0][i] == 1:
                break
            r1[i] = 1
        r2 = r1
        for i in range(1,m):
            r2[0] = r1[0]*(1 - x[i][0])
            for j in range(1,n):

                r2[j] = r1[j]*(1 - x[i][j]) + r2[j -1]*(1 - x[i][j])
            r1 = r2
            #print r2
        return r2[n-1]