[LeetCode]Pascal's Triangle II

Given an index k, return the k^th 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?

思考：维护数组ans，从后往前更新。

class Solution {

public:

    vector<int> getRow(int rowIndex) {

        vector<int> ans;

        ans.resize(rowIndex+1,0);

        ans[0]=1;

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

        {

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

            {

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

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

            }

        }

        return ans;

    }

};