Pascal's Triangle

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
          vector<vector<int>> vv;
          vector<int> v_arr[numRows+];

          if( numRows <= ) return vv;
          v_arr[].push_back();
          vv.push_back(v_arr[]);
          if(numRows == ) return vv;
          for(int row=;row<=numRows;row++){
              v_arr[row].push_back();       // 1 at begin
              int pre_len = v_arr[row-].size();
             for(int i=;i<pre_len-;i++){
                v_arr[row].push_back(v_arr[row-][i]+v_arr[row-][i+]);
             }
                v_arr[row].push_back();     //1 at end
                vv.push_back(v_arr[row]);
          }

          return vv;

    }
};