[LeetCode119]Pascal's 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?

求杨辉三角（也叫帕斯卡三角）的第n行

杨辉三角百度百科链接

http://baike.baidu.com/link?url=7YQlDvHXtPgr6zVk-Vaw1YG8TncQHUuSNoOrx8f61sj2kG-XCFGPmqvttAn8nleqW46fKGGWTY9tYyB9F7YVTK

代码：

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