LeetCode 63. Unique Paths II（唯一路径）

原题网址：https://leetcode.com/problems/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.
方法：动态规划。

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