[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.

https://oj.leetcode.com/problems/unique-paths-ii/

思路：同Unique Paths一样，也是DP，障碍物特殊处理：

初始化时，第一行和第一列，如果有障碍，则后面都不可达。

计算其他格子时，有障碍的情况为0即可。

public class Solution {

public int uniquePathsWithObstacles(int[][] obstacleGrid) {
if (obstacleGrid == null || obstacleGrid.length == 0)
return 0;
int m = obstacleGrid.length;
int n = obstacleGrid[0].length;

int[][] step = new int[m]
;

int i, j;
for (i = 0; i < m; i++) {
if (obstacleGrid[i][0] == 1)
break;
else
step[i][0] = 1;

}
for (i = 0; i < n; i++) {
if (obstacleGrid[0][i] == 1)
break;
else
step[0][i] = 1;
}

for (i = 1; i < m; i++)
for (j = 1; j < n; j++) {
if (obstacleGrid[i][j] == 0) {
step[i][j] = step[i - 1][j] + step[i][j - 1];
}

}

return step[m - 1][n - 1];
}

public static void main(String[] args) {
int[][] obstacleGrid = { { 0, 0, 0 }, { 0, 1, 0 }, { 0, 0, 0 } };
System.out.println(new Solution().uniquePathsWithObstacles(obstacleGrid));
}

}

View Code

参考：

/article/1347530.html

/article/1347528.html