Leetcode 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： 类似unique path，使用DP。区别在于怎么处理障碍物。如果obstacleGrid[i,j] == 1，那么显然DP[i,j] = 0。

 1 class Solution(object):
 2     def uniquePathsWithObstacles(self, obstacleGrid):
 3         """
 4         :type obstacleGrid: List[List[int]]
 5         :rtype: int
 6         """
 7         m = len(obstacleGrid)
 8         n = len(obstacleGrid[0])
 9         
10         dp = [[0]*n for x in range(m)]
11         
12         if obstacleGrid[0][0] == 1:
13             return 0
14         else: 
15             dp[0][0] = 1
16             
17         for i in range(m):
18             for j in range(n):
19                 if i == 0 and j == 0:
20                     continue
21                 if obstacleGrid[i][j] == 1:
22                     dp[i][j] = 0
23                 else:
24                     if j == 0:
25                         dp[i][j] = dp[i-1][j]
26                     elif i == 0:
27                         dp[i][j] = dp[i][j-1]
28                     else:
29                         dp[i][j] = dp[i][j-1] + dp[i-1][j]
30         
31         return dp[-1][-1]
32

 

posted @ 2017-01-25 14:23  lettuan  阅读(145)  评论(0)  编辑  收藏  举报