Leetcode 118

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