Pascal's Triangle II 第k个数字的排列 杨辉三角形

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> ans(rowIndex+1);//初始化为0
        ans[0]=1;
        for(int i=1;i<=rowIndex;i++)
        {
            for(int j=i;j>0;j--)
            {
                if(j==i)
                    ans[j]=1;
                else
                    ans[j]=ans[j-1]+ans[j];
            }
        }
        return ans;
    }
};