题目：
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.
思路：
动态规划，遇到1就设置为0
package dp; public class UniquePathsII { public int uniquePathsWithObstacles(int[][] obstacleGrid) { int m; int n; if (obstacleGrid == null || (m = obstacleGrid.length) == 0 || (n = obstacleGrid[0].length) == 0) return 0; int[][] dp = new int[m][n]; dp[0][0] = obstacleGrid[0][0] == 0 ? 1 : 0; for (int i = 1; i < m; ++i) dp[i][0] = obstacleGrid[i][0] == 0 ? dp[i - 1][0] : 0; for (int i = 1; i < n; ++i) dp[0][i] = obstacleGrid[0][i] == 0 ? dp[0][i - 1] : 0; for (int i = 1; i < m; ++i) { for (int j = 1; j < n; ++j) { dp[i][j] = obstacleGrid[i][j] == 1 ? 0 : (dp[i - 1][j] + dp[i][j - 1]); } } return dp[m - 1][n - 1]; } public static void main(String[] args) { // TODO Auto-generated method stub int[][] grid = { {0,0,0}, {0,1,0}, {0,0,0} }; UniquePathsII u = new UniquePathsII(); System.out.println(u.uniquePathsWithObstacles(grid)); } }