Pascal's Triangle

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]]

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代码：

class Solution {public:    vector<vector<int>> generate(int numRows) {        vector<vector<int>> v1;        if(numRows==0)  return v1;        v1.push_back(vector<int>(1,1));        if(numRows==1) return v1;        v1.push_back(vector<int>(2,1));        if(numRows==2) return v1;        for(int i=3;i<numRows+1;++i)        {            vector<int> temp;            temp.push_back(1);            for(int j=1;j<v1.back().size();++j)            {                temp.push_back(v1.back()[j-1]+v1.back()[j]);            }            temp.push_back(1);            v1.push_back(temp);        }        return v1;    }};