[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;
    }
};