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？
例题：
输入:
[
[0,0,0],
[0,1,0],
[0,0,0]
]
输出: 2
第一行、第一列更新的技巧
class Solution(object):
def uniquePathsWithObstacles(self, obstacleGrid):
"""
:type obstacleGrid: List[List[int]]
:rtype: int
"""
m = len(obstacleGrid)
n = len(obstacleGrid[0])
if obstacleGrid[0][0] == 1:
return 0
obstacleGrid[0][0] = 1
for i in range(1,m):
obstacleGrid[i][0] = int(obstacleGrid[i][0] == 0 and obstacleGrid[i-1][0] == 1)
for j in range(1, n):
obstacleGrid[0][j] = int(obstacleGrid[0][j] == 0 and obstacleGrid[0][j-1] == 1)
for i in range(1,m):
for j in range(1,n):
if obstacleGrid[i][j] == 0:
obstacleGrid[i][j] = obstacleGrid[i-1][j] + obstacleGrid[i][j-1]
else:
obstacleGrid[i][j] = 0
return obstacleGrid[m-1][n-1]
