[leetcdoe] 119. Pascal's Triangle II 解题报告

题目链接：https://leetcode.com/problems/pascals-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：每一行除第一列和最后一列为1之外, 其他都是由其正上方一行和左边的和构成, 因此答案就很明显了

代码如下:

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<int> vec(rowIndex+1, 1);        for(int i = 2; i <= rowIndex; i++)            for(int j = i-1; j>=1; j--)                vec[j] = vec[j] + vec[j-1];        return vec;    }};