63. Unique Paths II

 1     public int uniquePathsWithObstacles(int[][] obstacleGrid) {
 2         if(obstacleGrid == null || obstacleGrid.length == 0 || obstacleGrid[0].length == 0) {
 3             return 0;
 4         }   
 5         int len = obstacleGrid[0].length;
 6         int[] res = new int[len];
 7         res[0] = 1;
 8         for(int i = 0; i < obstacleGrid.length; i++) {
 9             for(int j = 0; j < len; j++) {
10                 if(obstacleGrid[i][j] == 1) {
11                     res[j] = 0;
12                 } else {
13                     if(j > 0) {
14                         res[j] += res[j-1];
15                     }
16                 }
17             }
18         }
19         return res[len-1];
20     }