ADD:
DP Subject:100 DP formula
63. Unique Paths II
Medium

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

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.

Note: m and n will be at most 100.

Example 1:

Input:
[
  [0,0,0],
  [0,1,0],
  [0,0,0]
]
Output: 2
Explanation:
There is one obstacle in the middle of the 3x3 grid above.
There are two ways to reach the bottom-right corner:
1. Right -> Right -> Down -> Down
2. Down -> Down -> Right -> Right

BONUS:

1.for python for loop don't have actual meaning so even "_" this kinds of thing can also used in for loop

for _ in range(5):
    print(_)

 

dp = [[0] * n for _ in range(m)]

using this method to initialize the two-dimension array

2.Python strip() 方法用于移除字符串头尾指定的字符(默认为空格)

import sys


class Solution(object):
    def uniquePathsWithObstacles(self, obstacleGrid):
        """
        :type obstacleGrid: List[List[int]]
        :rtype: int
        """
        m,n=len(obstacleGrid),len(obstacleGrid[0])
        #attention:0*n first multiply n for m the rank easy confuse
        dp=[[0]*n for _ in range(m)]
        if obstacleGrid[0][0]==0:
            dp[0][0]=1
        for i in range(m):
            for j in range(n):
                if obstacleGrid[i][j]==0:
                    if i==j==0:
                        continue
                    dp[i][j]=dp[i-1][j]+dp[i][j-1]
        return dp[m-1][n-1]

solu=Solution()
#obstacleGrid=input()


myList2=[
  [0,0,0],
  [0,1,0],
  [0,0,0]
]
print(solu.uniquePathsWithObstacles(myList2))

 

posted on 2019-08-06 12:54  黑暗尽头的超音速炬火  阅读(143)  评论(0编辑  收藏  举报