118. Pascal's Triangle

题目：

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,

Return

[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]

思路：
Pascal三角形，每一行除首尾为1外其余均为上一样相邻两数的和

代码：

class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<vector<int>> res(0);
vector<int> ress;
if(numRows==0)
return res;
ress.push_back(1);
res.push_back(ress);
for(int i=2;i<=numRows;i++)
{
vector<int> temp;
temp.push_back(1);
for(int j = 0;j<ress.size()-1;j++)
{
temp.push_back(ress[j]+ress[j+1]);
}
temp.push_back(1);
res.push_back(temp);
ress = temp;

}
return res;
}
};