leetcode -- 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.

[解题思路]

本题与上题思路差不多，直接使用DP来解，唯一区别在对obstacle的处理上，当遇到obstacle时将该位置置为0

表示该位置不可以到达[m][n]

 1 public int uniquePathsWithObstacles(int[][] obstacleGrid) {
 2         // Start typing your Java solution below
 3         // DO NOT write main() function
 4         int m = obstacleGrid.length;
 5         int n = obstacleGrid[0].length;
 6         int[][] steps = new int[m+2][n+2];
 7         for(int i = 0; i < m; i++){
 8             for(int j = 0; j < n; j++){
 9                 steps[i][j] = 0;
10             }
11         }
12         steps[m][n+1] = 1;
13         for(int i = m; i >= 1; i--){
14             for(int j = n; j >= 1; j--){
15                 if(obstacleGrid[i - 1][j - 1] == 1){
16                     steps[i][j] = 0;
17                     continue;
18                 }
19                 steps[i][j] = steps[i+1][j] + steps[i][j+1];
20             }
21         }
22         return steps[1][1];
23     }