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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> vec(rowIndex+1,1);
        if(rowIndex <= 1) return vec;
        
        for(int i = 2; i <= rowIndex;i++)
        {
            for(int j = i-1; j >=1 ;j--)
            {
                vec[j] += vec[j-1];
            }
        }
        return vec;
    }
};

16 milli secs.

因为不需要返回所有数组，只用一个O(rowIndex)的数组即可。