LeetCode之Pascal's Triangle II

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,
Return [1,3,3,1].

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

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<int> rst;        if(rowIndex<0)  return rst;         rst.push_back(1);        for(int i=1;i<=rowIndex;i++){            rst.push_back(1);            for (int j = i/2; j >0; j--){                rst[j]=rst[j]+rst[j-1];            }           for (int m =1,n=i-1;n>m;--n,++m){                rst[n]=rst[m];            }        }         return rst;    }};