# 119.Pascals Triangle II

**119.Pascals Triangle II**

难度:Easy

> 给定一个非负索引 k，其中 k ≤ 33，返回杨辉三角的第 k 行。

![](https://i.loli.net/2019/05/06/5ccfe43c3388f.gif)

在杨辉三角中，每个数是它左上方和右上方的数的和。

```
示例:

输入: 3
输出: [1,3,3,1]
进阶：

你可以优化你的算法到 O(k) 空间复杂度吗？
```

优化空间复杂度，需要牺牲一定的时间复杂度，可以使用递归实现。

```
class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> res;
        if (rowIndex==0) 
        {
            res.push_back(1);
            return res;
        }
        if(rowIndex==1)
        {
            res.push_back(1);
            res.push_back(1);
            return res;
        }
        
        res=getRow(rowIndex-1);
        res.push_back(res[rowIndex-1]);
        for(int i=rowIndex-1;i>0;i--)
        {
            res[i]+=res[i-1];
        }
      
        return res;
    }
};
```

> 执行用时 : 8 ms, 在Pascal's Triangle II的C++提交中击败了95.90% 的用户 内存消耗 : 9.2 MB, 在Pascal's Triangle II的C++提交中击败了5.14% 的用户


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