【leetcode】Pascal's Triangle II

Question：

 

Given an index k, return the k^th 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?

 

Anwser 1：   

 

class Solution {

public:

    vector<int> getRow(int rowIndex) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        vector<int> ret;

        

        for(int i = 0; i <= rowIndex; i++){

            if(i == 0) {

                ret.push_back(1);

                continue;

            }            

            

            for(int j = i; j >= 0; j--){    // from end to begin

                if(j == 0) {

                    ret[0] = 1;

                } else if(j == i){

                    ret.push_back(1);

                }else {

                    ret[j] = ret[j-1] + ret[j];

                }

            }

        }

        

        return ret;

    }

};