[LeetCode] Unique Paths II

Problem:

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.

Solution:O(m*n)

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