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 (m <= 0 || n <= 0) {
        	return 0;
        }
        if(obstacleGrid[0][0] == 1 || obstacleGrid[m-1][n-1] == 1)  
            return 0; 
        int[][] res = new int[m][n];
        res[0][0] = 1;
        for (int i = 1; i < m; i++) {
        	if (obstacleGrid[i][0] == 1) {
        		res[i][0] = 0;
        	} else {
        		res[i][0] = res[i-1][0];
        	}
        }
        for (int i = 1; i < n; i++) {
        	if (obstacleGrid[0][i] == 1) {
        		res[0][i] = 0;
        	} else {
        		res[0][i] = res[0][i-1];
        	}
        }
        for (int i = 1; i < m; i++) {
        	for (int j = 1; j < n; j++) {
        		if (obstacleGrid[i][j] == 1) {
        			res[i][j] = 0;
        		} else {
        			res[i][j] = res[i-1][j] + res[i][j-1];
        		}
        	}
        }
        return res[m-1][n-1];
    }
}