Unique Paths II

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

本题不是特别的难，只需要判断下是否空格为1，如果为1，则sum为0，不是1的话，那么就和第一题一样。

代码：

class Solution {
public:
//https://leetcode.com/problems/unique-paths-ii/
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        const int m=obstacleGrid.size(),n=obstacleGrid[0].size();
        if(obstacleGrid[0][0]==1||obstacleGrid[m-1][n-1]==1){
            return 0;
        }
        int sum[m][n];
        sum[0][0]=1;
        for(int i=1;i<n;i++){
            sum[0][i]=obstacleGrid[0][i]==0?sum[0][i-1]:0;
        }//如果等于1，直接为0；如果不为1，和前面相同
        for(int i=1;i<m;i++){
            sum[i][0]=obstacleGrid[i][0]==0?sum[i-1][0]:0;
        }
        
        for(int i=1;i<m;i++){
            for(int j=1;j<n;j++){
                sum[i][j] = obstacleGrid[i][j]==0?(sum[i-1][j]+sum[i][j-1]):0;
            }
        }
        
        return sum[m-1][n-1];
    }
};