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.

public class Solution {
    public int uniquePathsWithObstacles(int[][] grid) {
        if(grid == null || grid.length == 0 || grid[0].length == 0) return 0;
        int m = grid.length;
        int n = grid[0].length;
        int[][] dp= new int[m][n];
        for(int k=0; k<n;k++){
            if(grid[0][k] == 0) dp[0][k] = 1;
            else break;
        }
        for(int k=0; k<m;k++){
            if(grid[k][0] == 0) dp[k][0] = 1;
            else break;
        }

        for(int i=1; i< m;i++){
            for(int j=1;j<n;j++){
                if(grid[i][j] == 1){
                    dp[i][j] = 0;
                }else{
                    dp[i][j] = dp[i-1][j] + dp[i][j-1];
                }
            }
        }

        return dp[m-1][n-1];
    }
}