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]

public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        int[][] steps = new int[m+2][n+2];
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                steps[i][j] = 0;
            }
        }
        steps[m][n+1] = 1;
        for(int i = m; i >= 1; i--){
            for(int j = n; j >= 1; j--){
                if(obstacleGrid[i - 1][j - 1] == 1){
                    steps[i][j] = 0;
                    continue;
                }
                steps[i][j] = steps[i+1][j] + steps[i][j+1];
            }
        }
        return steps[1][1];
    }