Pascal's Triangle II

来源：Leetcode

原帖：https://oj.leetcode.com/problems/pascals-triangle-ii/

题目：
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?

代码：

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