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.题意：和前一题不同，这题中间的网格有障碍，求不同走法总数。思路：仍然是动态规划，但是一遇到障碍就置0.代码：class Solution {
public:
int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
int m=obstacleGrid.size();
int n=obstacleGrid[0].size();
int f[1001][1001];
if(obstacleGrid[0][0])
return 0;
if(m==1&&n==1&&obstacleGrid[0][0]==0)
return 1;
f[0][0]=1;
for(int i=1;i<n;i++)
f[0][i]=!obstacleGrid[0][i]?f[0][i-1]:0;
for(int i=1;i<m;i++)
f[i][0]=!obstacleGrid[i][0]?f[i-1][0]:0;
for(int i=1;i<m;i++)
for(int j=1;j<n;j++)
f[i][j]=!obstacleGrid[i][j]?f[i-1][j]+f[i][j-1]:0;
return f[m-1][n-1];
}
};