Pascal’s Triangle II (Easy)

Description

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?

Analysis

使用O(k)的空间来实现帕斯卡三角,从后往前递推即可

My Solution

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//C++
class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int>ans(rowIndex+1,1);
        for(int i = 2;i<=rowIndex;i++){
            for(int j = i-1;j>=1;j--){
                ans[j]+=ans[j-1];
            }
        }
        return ans;
    }
};