leetcode118 C++ 12ms 杨辉三角

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> res;
        if(numRows<=0){
            return res;
        }
        else if(numRows==1){
            return {{1}};
        }
        res = {{1}};
        vector<int> curr_row;
        int r=1;
        while(r < numRows){
            r++;
            curr_row.clear();
            curr_row.push_back(1);
            for(int i=1;i<r-1;i++){
                curr_row.push_back(res[r-2][i-1] + res[r-2][i]);
            }
            curr_row.push_back(1);
            res.push_back(curr_row);
        }
        return res;
        
    }
};