leetcode 119. Pascal's Triangle II

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<int> ans1,ans2,&res1=ans1,&res2=ans2;        res1.push_back(1);        for(int i=0;i < rowIndex; i++){            res2.clear();            res2.push_back(1);            for(int j = 0;j < res1.size()-1;j++)                res2.push_back(res1[j]+res1[j+1]);            res2.push_back(1);            swap(res1,res2);        }        return res1;    }};