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];
}
};