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?

思路：空间小了O（K）.

question：下面的代码中每行的最后一列的1是什么时候加进去的呢？

class Solution {
public:
    vector<int> getRow(int rowIndex) {
       vector<int> array;
        for (int i = 0; i <= rowIndex; i++) 
        {
            for (int j = i-1; j > 0; j--)
            {
                array[j] = array[j-1] + array[j];
            }
            array.push_back(1);
        }
        return array;
    }
};