leetcode[119]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> res;

        if(rowIndex<0)return res;

        res.resize(rowIndex+1);

        res[0]=1;

        for(int i=1;i<=rowIndex;i++)

        {

            for(int j=i;j>=0;j--)

            {

                if(j==0||j==i)res[j]=1;

                else res[j]=res[j]+res[j-1];

            }

        }

        return res;

    }

};