leetcdoe 帕斯卡尔三角形2 Pascal's Triangle II

帕斯卡尔三角形：

[

[1],

[1,1],

[1,2,1],

[1,3,3,1],

[1,4,6,4,1]

]

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,

Return [1,3,3,1].

class Solution {
public:
vector<int> getRow(int rowIndex) {
vector<vector<int>> res(rowIndex+1);
//if(rowIndex<0)return res[0];
res[0].push_back(1);
int i,j;
for(i=1;i<res.size();i++)
{
for(j=0;j<i+1;j++)
{if(j==0||j==i)res[i].push_back(1);
else res[i].push_back(res[i-1].at(j-1)+res[i-1].at(j)); }
}
return res[rowIndex];  }
};