118. Pascal's Triangle

    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> res;
        if(numRows<=0) return res;
        res.assign(numRows,vector<int>(1,1));
        for(int i=1;i<numRows;i++){
           for(int j=1;j<res[i-1].size();j++)
               res[i].push_back(res[i-1][j]+res[i-1][j-1]);
            res[i].push_back(1);
        }
        return res;
    }