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[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][n]; 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)); }}
参考：
http://blog.csdn.net/kenden23/article/details/17303497
http://blog.csdn.net/kenden23/article/details/17317805
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