[LeetCode]Pascal's Triangle II

题目描述:

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?

解题思路:

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> result;
        result.push_back(1);
        
        ++rowIndex;
        long s = 1;
        if (rowIndex == 1) {
            return result;
        }
        
        for (int j = 1; j <= rowIndex - 2; ++j) {
            result.push_back(s = ((rowIndex - j) * s) / j);
        }
        
        result.push_back(1);
        
        return result;
    }
};