【leetcode】119. Pascal's Triangle II

题目：
Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal’s triangle.

Note that the row index starts from 0.

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

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思路：
直接看图就好。规律很明显。

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代码实现：

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