119. Pascal's Triangle II

题目：

Given an index k, return the kth

For example, given k = 3,

Return ​​[1,3,3,1]​​.

Note:
Could you optimize your algorithm to use only O(k) extra space?

思路：

本题由​​上一篇博客​​衍生而来，方法同上一篇博客，只是不需要额外数组来存储所有vector数组

代码：

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