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;    }};