【Leetcode】之Unique Paths II

一.问题描述

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.

二.我的解题思路

之前已经采用动态规划算法做过上一题，那么就直接在上一题程序的基础上去做本题。我就加了几个if条件来判断是否有障碍物，然后就AC了。程序如下：

class Solution {
public:
int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
int m = obstacleGrid.size();
if(m<=0) return 0;
int n = obstacleGrid[0].size();
if(m==1 && n==1 && obstacleGrid[0][0]==0) return 1;
if( n<=0) return 0;
int res[m+1][n+1];
for(int i=0;i<=m;i++) res[i][0]=0;
for(int i=0;i<=n;i++) res[0][i]=0;
for(int i=1;i<=m;i++){
for(int j=1;j<=n;j++){
if(obstacleGrid[m-i][n-j]==1) res[i][j]=0;
else res[i][j]=res[i-1][j]+res[i][j-1];
if(i==1 && j==1 && obstacleGrid[m-1][n-1]==0) res[i][j]=1;
if(i==1 && j==1 && obstacleGrid[m-1][n-1]==1) return 0;
}
}
return res[m]
;
}
};