[LeetCode]Unique Paths [email protected]

Unique Paths II

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?

Example

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

Solution

class Solution:
    def uniquePathsWithObstacles(self, obstacleGrid: List[List[int]]) -> int:
        m, n = len(obstacleGrid), len(obstacleGrid[0])
        dp = [0]*n
        dp[0] = 1
        for i in range(m):
            for j in range(n):
                if obstacleGrid[i][j]==1:
                    dp[j] = 0
                elif j>0:
                    dp[j] += dp[j-1]
        return dp[-1]