Leetcode#118 Pascal's Triangle

 1 vector<vector<int> > generate(int numRows) {
 2         vector<vector<int> > res;
 3         
 4         if (numRows <= 0)
 5             return res;
 6             
 7         res.push_back(vector<int>(1, 1));
 8         while (--numRows) {
 9             vector<int> layer;
10             layer.push_back(1);
11             for (int i = 0; i + 1 < res.back().size(); i++)
12                 layer.push_back(res.back()[i] + res.back()[i + 1]);
13             layer.push_back(1);
14             res.push_back(layer);
15         }
16         
17         return res;
18 }