LeetCode_pascals-triangle-ii

https://leetcode.com/problems/pascals-triangle-ii/
思路：从数组最后一个计算，向前迭代；

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