[LeetCode]Pascal's Triangle II

Pascal's Triangle II

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?

 

O(k)的空间，那么就直接初始化，然后按照Pascal's Triangle的规律，计算。

由于覆盖的问题，从后往前计算就可以避免。

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> result(rowIndex+1,1);
        for(int i=0;i<=rowIndex;i++)
        {
            for(int j=i-1;j>0;j--)
            {
                result[j] = result[j-1]+result[j];
            }
        }
        return result;
    }
};