LeetCode_OJ【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.

做了62题很显然这道题也要用动规来做，设置steps[][]数组来记录可行解的个数。steps[i][j]表示从(i,j)到(m-1,n-1)的可行解的个数。

显然steps[i][j] = steps[i+1][j] + steps[i][j+1]，当然这题要考虑障碍物的影响。

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