# 0063. Unique Paths II
###### tags: `Leetcode` `Medium` `动态规划`
Link: https://leetcode.com/problems/unique-paths-ii/

## 思路
和上一题差不多，但要注意i = 0和j = 0一行一列的赋值
以及可以用Line17代替Line 11-16虽然run起来结果一样，但是更省力~
并且要注意**有些时候动态规划的题目不需要重新再建一个array来存结果或者不需要一个跟input一样大的array来存结果**（如62题）
## Code

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

## Result
Runtime: 0 ms, faster than **100.00%** of C++ online submissions for Unique Paths II.
Memory Usage: 7.5 MB, less than **96.49%** of C++ online submissions for Unique Paths II.