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.

public class Solution {
public int uniquePathsWithObstacles(int[][] obstacleGrid) {
int m=obstacleGrid.length;
int n=obstacleGrid[0].length;
if(obstacleGrid==null)
return 0;
if(m<=0||n<=0)
return 0;
if(obstacleGrid[0][0]==1)
return 0;
if(obstacleGrid[m-1][n-1]==1)
return 0;
int[][] f=new int[m+1][n+1];
for(int i=0;i<=m;i++)
f[i]
=0;
for(int i=0;i<=n;i++)
f[m][i]=0;
for(int i=0;i<m;i++)
for(int j=0;j<n;j++)
{
if(obstacleGrid[i][j]==1)
f[i][j]=0;
}
for(int i=m-1;i>=0;i--)
for(int j=n-1;j>=0;j--)
{
if(obstacleGrid[i][j]==0)
f[i][j]=f[i+1][j]+f[i][j+1];
else f[i][j]=0;
f[m-1][n-1]=1;
}
return f[0][0];
}
}