LeetCode_DP_Unique Paths II

Unique Paths II

一、题目说明

这道题目和 Unique Paths （http://blog.csdn.net/glDemo/article/details/48166685）不同之处在于有了障碍物的情况，也是求有多少条路线从左上角到右下角。

二、思路

其实主要思路和 Unique Paths 一样，只不过要在遍历中处理碰到障碍物时，到这个点的路径数为 0。

三、java代码

public class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;

        if(obstacleGrid[0][0] == 1 || obstacleGrid[m-1][n-1] == 1)
            return 0;

        for(int i=0; i<m; i++) {
            for(int j=0; j<n; j++) {
                if(obstacleGrid[i][j] == 1) 
                    obstacleGrid[i][j] = 0;
                else if(i==0 && j==0)
                    obstacleGrid[i][j] = 1;
                else if(i==0) 
                    obstacleGrid[i][j] = obstacleGrid[i][j-1];//只能从left递推
                else if(j==0)
                    obstacleGrid[i][j] = obstacleGrid[i-1][j];
                else 
                    obstacleGrid[i][j] = obstacleGrid[i-1][j] + obstacleGrid[i][j-1];
            }
        }
        return obstacleGrid[m-1][n-1];

    }
}