Unique Paths II - Leetcode

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;
		int[] f = new int[n];

        f[0] = obstacleGrid[0][0] == 1?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 {
					if (j == 0)
						f[j] = f[j];
					else
						f[j] = f[j] + f[j - 1];
				}
			}
		return f[n - 1];
    }
}