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;    }