[LeetCode] 068: Pascal\'s Triangle II

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?

class Solution {
   
public:
	vector<int> getRow(int rowIndex) {
   
		// Note: The Solution object is instantiated only once and is reused by each test case.
		vector<int> res;
		if(rowIndex < 0)return res;

		for(int i = 0; i <= rowIndex; ++i){
   
			if(i == 0){
   
				res.push_back(1);
			}
			else{
   
			    long long pre = res.back();
				if((rowIndex+1)%2 != 0 || i != (rowIndex+1)/2){
   
					res.push_back(pre * (rowIndex+1-i) / i);
				}
				else{
   
					res.push_back(pre);
				}
			}
		}
		return res;
	}
};