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Leetcode: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.

分析:动态规划+滚动数组。代码如下:

class Solution {public:    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {        int m = obstacleGrid.size();        if(m == 0) return 0;        int n = obstacleGrid[0].size();        if(n == 0) return 0;                vector<int> f(n, 0);        if(obstacleGrid[0][0] == 1)            return 0;                f[0] = 1;        for(int i = 0; i < m; i++)            for(int j = 0; j < n; j++)                if(obstacleGrid[i][j] == 1)                    f[j] = 0;                else f[j] += (j == 0)?0:f[j-1];                return f[n-1];    }};

 

Leetcode:Unique Paths II