119. Pascal's Triangle II

Problem

Given a non-negative index k where k ≤ 33, return the k^th index row of the Pascal's triangle.
Note that the row index starts from 0.

image.png

In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example

Input: 3
Output: [1,3,3,1]

Follow up:
Could you optimize your algorithm to use only O(k) extra space?

Code

static int var= [](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();
class Solution {
public:
    vector getRow(int rowIndex) {
        vector res(rowIndex+1,0);
        if(rowIndex>=0)
            res[0] = 1;
        for(int i=0;i<=rowIndex;i++){
            for(int j=i;j>0;j--){
                res[j] += res[j-1];
            }
        }
        return res;
    }
};

Result

119. Pascal's Triangle II.png