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